Approximate date of commencement of proposed sale to the
public: As soon as practicable after the effective date hereof.

If any of the securities being registered
on this form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act, check the following
box. ¨

If this form is filed to register additional
securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities
Act registration statement number of the earlier effective registration statement for the same offering. ¨

If this form is a post-effective amendment
filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement
number of the earlier effective registration statement for the same offering. ¨

If this form
is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the
Securities Act registration statement number of the earlier effective registration statement for the same offering. ¨

Indicate
by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller
reporting company. Large accelerated filer¨ Accelerated
filer¨ Non-accelerated filer¨
Smaller reporting company:x

The registrant hereby amends this registration statement
on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which
specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities
Act of 1933, as amended, or until this registration statement shall become effective on such date as the Commission, acting pursuant
to said Section 8(a), may determine.

The information in this prospectus is not complete
and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission
is effective. This prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities
in any state or other jurisdiction where the offer or sale is not permitted.

SUBJECT TO COMPLETION,
DATED April 23, 2014

PRELIMINARY PROSPECTUS

2,000,000 shares of Common Stock

Tecogen Inc. is offering 2,000,000 shares
of its common stock.

Prior to this offering, there has not been
a public market for our common stock. We expect that the public offering price will be between $4.75 and $5.75 per share. We have
applied to list our common stock on the NASDAQ Capital Market under the symbol “TGEN”.

The Company has retained Scarsdale Equities
LLC, or the Placement Agent, to act as the exclusive placement agent for the offering. The Placement Agent has agreed to use its
commercially reasonable efforts to solicit offers to purchase shares of Common Stock. The Placement Agent is not purchasing or
selling any shares of Common Stock pursuant to this offering, nor are we requiring any minimum purchase of any specific number
of shares. Because there is no minimum offering amount required as a condition to the closing of the offering, the actual public
offering amount, placement agent fees and proceeds to us are not presently determinable and may be substantially less than the
amounts set forth below. See “Plan of Distribution” beginning on page 81 of this prospectus for more information regarding
these arrangements.

We are an “emerging growth
company,” as that term is used in the Jumpstart Our Business Startups Act of 2012, or the JOBS Act, and, as such, have
elected to comply with certain reduced public company reporting requirements for this prospectus and future filings. See
“Prospectus Summary — Implications of Being an Emerging Growth Company.”

Investing in our common stock involves
a high degree of risk. See “Risk Factors” beginning on page 8 of this prospectus for a discussion of information that
should be considered in connection with an investment in our common stock.

Neither the Securities and Exchange Commission,
nor any state securities commission has approved or disapproved these securities or determined if this prospectus is truthful or
complete. Any representation to the contrary is a criminal offense.

Maximum Offering

Per Share

Total

Public offering price

$

$

Placement agent fees

$

$

Proceeds to us (before expenses)(1)

$

$

(1)

We have agreed to reimburse the Placement Agent for certain expenses. See “Plan of Distribution.”

We expect that delivery of the Common Stock
sold in the offering will be made on or about , 2014.

SCARSDALE
EQUITIES

The date of this prospectus
is , 2014.

TABLE OF CONTENTS

Page

Prospectus Summary

1

The Offering

5

Summary Consolidated Financial Data

6

Risk Factors

8

Special Note Regarding Forward-Looking Statements

20

Use of Proceeds

21

Dividends

21

Determination of Offering Price

22

Capitalization

23

Dilution

25

Selected Consolidated Financial Data

26

Management’s Discussion and Analysis of Financial Condition and Results of Operations

26

Business

32

Management and Governance

58

Executive Officer and Director Compensation

63

Principal Stockholders

70

Certain Relationships and Related Transactions

72

Description of Common Stock

77

Outstanding Securities and Shares Eligible for Future Sale

79

Plan of Distribution

81

Experts

83

Legal Matters

84

Where You Can Find Additional Information

84

Index of Financial Statements

F-1

You should rely only on the information
contained in this prospectus and any free writing prospectus prepared by or on behalf of us or to which we have referred you. Neither
we nor the Placement Agent have authorized anyone to provide you with information that is different. We are offering to sell our
common stock, and seeking offers to buy our common stock, only in jurisdictions where offers and sales are permitted.

We further note that the representations,
warranties and covenants made by us in any agreement that is filed as an exhibit to the registration statement of which this prospectus
forms a part were made solely for the benefit of the parties to such agreement, including, in some cases, for the purpose of allocating
risk among the parties to such agreements, and should not be deemed to be a representation, warranty or covenant to you. Moreover,
such representations, warranties or covenants were accurate only as of the date when made. Accordingly, such representations, warranties
and covenants should not be relied on as accurately representing the current state of our affairs.

For investors outside of the United States:
Neither we nor the Placement Agent have done anything that would permit this offering or possession or distribution of this prospectus
in any jurisdiction where action for that purpose is required, other than in the United States. You are required to inform yourselves
about and to observe any restrictions relating to this offering and the distribution of this prospectus.

In this prospectus, unless the context
otherwise requires, “Tecogen,” the “Company,” “we,” “us,” or “our”
refer to Tecogen Inc. and its subsidiary.

This prospectus includes statistical, market
and industry data and forecasts that we obtained from publicly available information and independent industry publications and
reports that we believe to be reliable sources. These publicly available industry publications and reports generally state that
they obtain their information from sources that they believe to be reliable, but they do not guarantee the accuracy or completeness
of the information. Although we believe that these sources are reliable, we have not independently verified the information contained
in such publications.

PROSPECTUS SUMMARY

The following summary highlights information
contained elsewhere in this prospectus. It is not complete and does not contain all of the information that you should consider
before investing in our common stock. You should read the entire prospectus carefully, especially the risks of investing in our
common stock discussed under “Risk Factors” and our consolidated financial statements and accompanying notes. In this
prospectus, unless the context otherwise requires, “Tecogen,” “Company,” “we,” “us,”
or “our,” refer to Tecogen Inc. and its subsidiaries.

Company Overview

Tecogen designs, manufactures, sells,
and services systems that produce electricity, hot water, and air conditioning for commercial installations and buildings and industrial
processes. Our systems, powered by natural gas engines, drive electricity generators or compressors, which reduce the amount of
electricity purchased from local utilities. Because our systems are designed to capture waste engine heat, they tend to be more
energy efficient since otherwise-wasted energy can be used for water heating, space heating and/or air conditioning. The relative
costs of natural gas and electricity at a proposed system site determine whether a system is economically efficient as well as
energy efficient. This type of cogeneration technology is referred to as combined heat and power, or CHP.

Tecogen manufactures three types of
CHP products:

•

Cogeneration units that supply electricity and hot water;

•

Chillers that provide air-conditioning and hot water; and

•

High-efficiency water heaters.

All of our products are standardized,
modular, small-scale CHP products that reduce energy costs, carbon emissions, and dependence on the electric grid. Market drivers
include the price of natural gas, local electricity costs, and governmental energy policies, as well as customers’ desire
to become more socially responsible. Traditional customers for our cogeneration and chiller systems include hospitals and nursing
homes, colleges and universities, health clubs and spas, hotels and motels, office and retail buildings, food and beverage processors,
multi-unit residential buildings, laundries, ice rinks, swimming pools, factories, municipal buildings, and military installations;
however, the economic feasibility of using our systems is not limited to these customer types. We have shipped approximately 2,000
units, some of which have been operating for almost 25 years. We have 69 full-time employees and three part-time employees, including
six sales and marketing personnel and 40 service personnel.

Our Technology

Our CHP technology uses low-cost, mass-produced
engines manufactured by General Motors Company, or GM, or Ford Motor Company, or Ford, which we modify to run on natural gas. Because
our systems are fueled by natural gas, they typically produce lower levels of “criteria” air pollutants (those that
are regulated by the Environmental Protection Agency, or EPA, because they can harm human health and the environment) compared
with systems fueled by propane, gasoline, distillates, or residual fuel oil. We offer our new advanced emission system, Ultra,
as an option in our CHP systems. With Ultra, our CHP products have achieved emission levels that qualify under strict existing
and proposed California emission standards. Other emerging technologies, such as fuel cells, may also meet those standards, but
we are not aware that any appear economically viable at this time.

1

Our products are designed as compact
modular units that are intended to be applied in multiples when utilized for larger CHP plants. Approximately 68% of our CHP modules
are installed in multi-unit sites ranging up to 12 units. This approach has significant advantages over utilizing single, larger
units, such as building placement in constrained urban settings and redundancy during service outages. Redundancy is particularly
relevant in regions where the electric utility has formulated tariff structures that have high “peak demand” charges.
Such tariffs are common in many areas of the United States, and are applied by such utilities as Southern California Edison, Pacific
Gas and Electric, Consolidated Edison of New York, and National Grid of Massachusetts. Because these tariffs assess customers’
peak monthly demand charge over a very short interval (typically only 15 minutes), a brief service outage for a system comprised
of a single unit is highly detrimental to the monthly savings of the system. For multiple unit sites, a full system outage is less
likely and consequently these customers have a greater probability of capturing peak demand savings.

Our in-licensed microgrid technology
enables our InVerde CHP product to provide backup power in the event of power outages that may be experienced by local,
regional, or national grids.

Our 65.0%-owned subsidiary Ilios, Inc.,
which does business under the name Ilios Dynamics in Massachusetts, or Ilios, has developed and distributes a line of high-efficiency
water heaters. Ilios technology is designed to capture available energy in the environment due to ambient temperature differences.
The physical laws of thermodynamics determine the portion of this available energy that can be theoretically captured. If the cost
of capturing a portion of that available energy is less than the value of that energy, additional system efficiencies may be obtained.
Thus, Ilios systems in certain cases may be more efficient than conventional boilers in commercial installations and industrial
processes.

Markets, Customers, and Suppliers

Our CHP products are sold directly
to customers by our in-house marketing team and by established sales agents and representatives, including American DG Energy Inc.,
or American DG Energy, and EuroSite Power Inc., or EuroSite Power, which are affiliated companies. Our principal engine supplier
is GM, and the other principal components of our CHP systems are also mass-produced. Other than service revenue, our products generally
do not produce recurring revenue as they typically constitute a one-time capital expenditure by a customer. We do not consider
ourselves dependent on one or a few customers, including our affiliated customers, American DG Energy and EuroSite Power. We strive
to obtain long-term service contracts for the products we manufacture through our factory-owned service centers in California,
the Midwest, and the Northeast United States. Between 2007 and 2012, approximately 68% of our installations also included service
contracts.

Strategy

While we believe that our products
and services provide efficient solutions to customers throughout the United States and around the world, our strategy for increased
revenue and profitability is to expand our operations in our existing territories where we perceive the demand for our products
and services is strongest, and where our products have particular advantages over our competition. Specifically, our CHP systems
provide energy-efficient power with technically superior emissions control, while also serving as backup power that may allow customers
in some areas to provide surplus power to an electrical grid. Our sales and technical staff operate from our existing service centers
in California and the Northeast. These regions have strict emissions regulations, which favor our products equipped with our Ultra
low-emission technology. Also, these regions have high peak demand rates, which favor utilization of our modular units in groups
so as to assure redundancy and peak demand savings, as discussed above. Some of these regions also have generous rebates that improve
the economic viability of our systems. We will also focus on customers that value our microgrid technology that enables the CHP
plant to serve the facility to provide backup power during outages. Our sales staff will support our existing sales channels, but
will also focus on selling complete design and installation services for customers in these regions. We believe that these design
and build services, or turnkey services, will expand our sales significantly because they increase revenue per unit sale substantially,
as they include the portion of the sale related to installation. We believe that turnkey installation services will improve our
service contract retention from its current rate of 68% between 2007 and 2012, to a near universal proportion. Moreover, we see
the turnkey model as a vehicle to expand our service offering to customers to include portions of the system outside of our factory
produced module that may improve the long-term operation of the CHP plant. Such items might include ancillary pumps, controls,
and heat exchangers, among other components.

2

Our business model of establishing
satellite service, sales, and installation centers will be our strategy in emerging domestic markets such as the mid-Atlantic region
and areas in the Midwest. For our overseas markets we will continue to develop regional allies for sales and service, such as EuroSite
Power in the United Kingdom, and our analogous allies in other international markets such as Mexico and Australia.

In markets we have identified to focus
our attention, we will continue our strategy of engaging the consulting engineering community through direct contact and also through
engineering societies and trade shows. Our sales staff will engage building owners and their management companies to explain the
energy-efficient products and solutions we offer with the goal of providing comprehensive turnkey installations.

Risks Associated with Our Business

Our business is subject to a number
of risks of which you should be aware before making an investment decision. These risks are discussed more fully in the “Risk
Factors” section of this prospectus immediately following this prospectus summary. These risks include, but are not limited
to, the following:

History of Operating Losses. For
each of our last five fiscal years and prior thereto, we have incurred annual operating losses. We expect this trend to continue
until such time that we can sell a sufficient number of systems and achieve a cost structure to become profitable, which may be
several years. We may not have adequate cash resources to reach the point of profitability, and we may never become profitable.
Even if we do achieve profitability, we may be unable to increase our sales and sustain or increase our profitability in the future.

Dependence on Key Suppliers. We
rely on a small number of key suppliers, and the loss one of them could materially and adversely affect our business. Further,
from time to time, shipments to us of key system components can be delayed because of industry-wide or other shortages, and the
components we receive may not meet our quality or cost requirements.

Dependence on Technology Development. Our
products incorporate proprietary technology, and our future success will depend upon our ability to continue to develop and provide
innovative products and product enhancements. The introduction of products embodying new technologies, and the shifting of customer
demands or changing industry standards, could render our existing products obsolete and unmarketable.

Changes in governmental regulation
could adversely affect us. We operate in a highly regulated business environment, and changes in regulation could
impose significant costs on us or could make our products less economical.

The economic viability of our projects
depends on the price spread between fuel and electricity. Variability of the price spread between fuel and electricity creates
a risk that our projects will not be economically viable and that potential customers will avoid such energy price risks.

There has been a material weakness
in our disclosure controls and procedures and in our internal control over financial reporting. Although we consider
the size of our accounting staff sufficient to meet our business needs, a need for improved controls and procedures surrounding
technical accounting practices, information technology, and financial reporting currently exists.

Our chief executive officer and
chief financial officer have responsibilities to affiliated companies. Our key executives spend a significant portion
of their time performing management functions for one or more of our affiliated companies. John N. Hatsopoulos is the Company’s
Chief Executive Officer and is also the Chief Executive Officer of American DG Energy. In the past Mr. Hatsopoulos has spent approximately
50% of his business time on the affairs of the Company. Although such amount varies widely depending on the needs of the business,
he has actively fulfilled all his duties as the Company’s CEO and feels confident that he will be able to continue fulfilling
such duties in the future. Bonnie Brown is the Company’s Chief Financial Officer and is also Chief Financial Officer of Ilios,
the Company’s majority-owned subsidiary.

3

Recent Developments

The U.S. Patent and Trademark Office,
or the U.S. PTO, has issued our patent relating to the assembly and method for reducing nitrogen oxides and hydrocarbons in exhausts
of internal combustion engines, which is the underlying process used in our Ultra low-emissions technology. The claims describe
a method of operating an engine exhaust treatment system that reduces certain “criteria” pollutants, the common air
pollutants determined to be hazardous to human health and regulated under the Environmental Protection Agency’s National
Ambient Air Quality Standards, to extremely low values by converting most of the toxic compounds in the engine exhaust to benign
compounds.

In order to satisfy our contractual
obligations, on February 6, 2014, we filed a registration statement on Form S-1 with the Securities and Exchange Commission, or
SEC, seeking to register 2,028,145 shares of our common stock for resale or other disposition by the selling stockholders named
therein. The offering by the selling stockholders is referred to in this prospectus as the secondary offering. Unless otherwise
explicitly stated, the information in this prospectus does not give effect to the secondary offering.

Implications of Being an Emerging Growth Company

We are an “emerging growth company,”
as that term is used in the JOBS Act and, for as long as we continue to be an “emerging growth company,” we may choose
to take advantage of exemptions from various reporting requirements applicable to other public companies but not to “emerging
growth companies,” including, but not limited to, not being required to comply with the auditor attestation requirements
of Section 404 of the Sarbanes-Oxley Act of 2002, or the Sarbanes-Oxley Act, reduced disclosure obligations regarding executive
compensation in our periodic reports and proxy statements, and exemptions from the requirements of holding a nonbinding advisory
vote on executive compensation and stockholder approval of any golden parachute payments not previously approved. We could be an
“emerging growth company” for up to five years, or until the earliest of (i) the last day of the fiscal year during
which our total annual gross revenues equal or exceed $1 billion (subject to adjustment for inflation), (ii) the last day of the
fiscal year following the fifth anniversary of our public offering, (iii) the date on which we have, during the previous three-year
period, issued more than $1 billion in non-convertible debt, or (iv) the date on which we are deemed a large accelerated filer
under the Securities Exchange Act of 1934, or the Exchange Act. We have chosen to “opt out” of the extended transition
periods available under the JOBS Act for complying with new or revised accounting standards, and intend to take advantage of the
other exemptions.

Corporate History

Tecogen began in the early 1960s as
a research division of Thermo Electron Corporation, now Thermo Fisher Scientific Inc., which is a publicly traded company listed
on the NYSE under the symbol TMO. In 2000, Tecogen was sold to private investors including Thermo Electron’s original founders,
Dr. George N. Hatsopoulos and John N. Hatsopoulos.

We were incorporated in the State of
Delaware on September 15, 2000. Our offices are located at 45 First Avenue, Waltham, Massachusetts 02451. Our telephone number
is 781-466-6400. Our Internet address is http://www.tecogen.com. The information on, or that may be accessed through, our
website is not incorporated by reference into this prospectus and should not be considered a part of this prospectus.

4

THE OFFERING

Common Stock being offered:

2,000,000 shares(1)

Common Stock to be outstanding after this offering:

17,155,200 shares(1)(2)

Use of proceeds:

We estimate that we will receive net proceeds of up to $9,341,000 from the sale of the shares of Common Stock offered hereby, after deducting the estimated placement agent fees and estimated offering expenses payable by us. We intend to use the net proceeds of this offering for working capital and general corporate purposes, including expanding our turnkey business, constructing a dedicated manufacturing facility for Ilios, expanding our low emission technology to other markets, and continuing product development.

A $0.25 increase (decrease) in the assumed public offering price of $5.25 per share would increase (decrease) the net proceeds of this offering by approximately $466,000, assuming that the number of shares we are offering, as set forth on the cover page of this prospectus, remains the same, after deducting the estimated placement agent fees and estimated offering expenses payable by us. We may also increase or decrease the number of shares we are offering. Each increase (decrease) of 100,000 shares in the number of shares we are offering would increase (decrease) the net proceeds to us from this offering by approximately $490,000, assuming that the assumed public offering price remains the same, and after deducting the estimated placement agent fees and estimated offering expenses payable by us.

Proposed NASDAQ Capital Market symbol:

TGEN

(1)

The number of shares that we sell assumes that we sell $10,500,000 of our common stock at a public offering price of $5.25
per share, the midpoint of the price range set forth on the cover page of this prospectus.

(2)

Unless we indicate otherwise, Common Stock outstanding after this offering is based on 15,155,200 shares of our common stock
outstanding as of December 31, 2013, assumes the sale of 2,000,000 shares in this offering; and excludes as of that date the
following:

◦

1,148,000 shares of Common Stock issuable upon the exercise of stock options outstanding prior to this offering under our stock
incentive plan, at a weighted average exercise price of $2.13 per share;

◦

58,683 shares of Common Stock available for future grants under our stock incentive plan;

◦

555,556 shares of Common Stock issuable pursuant to convertible debentures with an outstanding principal amount of $3,000,000
and a conversion price of $5.40 per share.

Except as otherwise noted, all information
in this prospectus gives retroactive effect to a one-for-four reverse split of our common stock effected on July 22, 2013.

5

SUMMARY CONSOLIDATED FINANCIAL DATA

The summary consolidated statements
of operations data for each of the years ended December 31, 2013 and 2012 and the summary consolidated balance sheet data as of
December 31, 2013 and 2012, have been derived from our audited consolidated financial statements that are included elsewhere
in this prospectus.

You should read this information together
with the consolidated financial statements and related notes and other information under “Management’s Discussion and
Analysis of Financial Condition and Results of Operations” included elsewhere in this prospectus.

Year Ended December 31,

Consolidated Statement of Operations Data:

2013

2012

Revenues

$

15,849,869

$

15,253,972

Cost of sales

10,819,741

9,388,898

Gross profit

5,030,128

5,865,074

Operating expenses

General and administrative

7,018,133

6,643,120

Selling

1,423,587

1,225,580

Aborted public offering costs

258,512

—

8,700,232

7,868,700

Loss from operations

(3,670,104

)

(2,003,626

)

Other income (expense)

Interest and other income

3,958

48,397

Interest expense

(141,065

)

(71,208

)

(137,107

)

(22,811

)

Loss before income taxes

(3,807,211

)

(2,026,437

)

Consolidated net loss

(3,807,211

)

(2,026,437

)

Less: Loss attributable to the noncontrolling interest

357,722

389,480

Net loss attributable to Tecogen Inc.

$

(3,449,489

)

$

(1,636,957

)

Net loss per share – basic and diluted

$

(0.26

)

$

(0.12

)

Weighted average shares outstanding – basic and diluted

13,385,155

13,135,071

As of December 31, 2012

As of December 31, 2013

Consolidated Balance Sheet Data:

Actual

Actual

Pro Forma(1)

Pro Forma As Adjusted(2)

Cash and cash equivalents

$

1,572,785

$

7,713,899

$

4,575,541

$

13,916,541

Short-term investments (restricted)

181,859

—

—

—

Working capital

4,078,704

5,565,789

5,578,089

14,919,089

Total assets

9,117,249

17,630,069

14,491,711

23,832,711

Total liabilities

4,334,214

10,564,176

7,814,834

7,814,834

Total stockholders’ equity

$

4,783,035

$

7,065,893

$

7,078,193

$

16,419,193

(1)

The pro forma consolidated balance sheet data in the table above gives effect to the private placement of 1,400 shares of
common stock at $4.50 per share from January 1 to January 17, 2014, the exercise of 5,000 options at $1.20 on February 18,
2014 and the repayment of debt to the Company's CEO on January 6, 2014 consisting of principal of $2,950,000 and accrued
interest of $200,658.

(2)

The pro forma as adjusted consolidated balance sheet data in
the table above gives effect to the sale of 2,000,000 shares of common stock in this
offering at an assumed public offering price of $5.25 per share, the midpoint of the
range set forth on the cover page of this prospectus, after deducting estimated placement
agent fees and estimated offering expenses payable by us. A $0.25 increase (decrease)
in the assumed public offering price of $5.25 per share would increase (decrease) each
of cash and cash equivalents, working capital, total assets and total stockholders’
equity by approximately $466,000, assuming the number of shares we are offering, as set
forth on the cover page of the prospectus, remains the same, after deducting the estimated
placement agent fees and estimated offering expenses payable by us. We may also increase
or decrease the number of shares we are offering. An increase (decrease) of 100,000 shares
in the number of shares we are offering would increase (decrease) each of cash and cash
equivalents, working capital, total assets and total stockholders’ equity by approximately
$490,000, assuming the assumed public offering price remains the same. The pro forma
as adjusted information is illustrative only, and we will adjust this information based
on the actual public offering price, number of shares offered and other terms of this
offering determined at pricing.

6

RISK FACTORS

The shares of Common Stock offered
hereby are highly speculative and should be purchased only by persons who can afford to lose their entire investment. You should
carefully consider the following risk factors and other information in this prospectus before deciding to purchase our common stock.
If any of the following risks actually occur, our business and financial results could be negatively affected to a significant
extent.

Risks Relating to Our Business

Our business faces many risks. The risks
described below may not be the only risks we face. Additional risks that we do not yet know of, or that we currently think are
immaterial, may also impair our business operations or financial results. If any of the events or circumstances described in the
following risks occurs, our business, financial condition or results of operations could suffer and the trading price of our common
stock could decline. Investors and prospective investors should consider the following risks and the information contained under
the heading ''Cautionary Note Concerning Forward-Looking Statements'' before deciding whether to invest in our securities.

Our operating history is characterized
by net losses. We anticipate incurring further losses, and we may never become profitable.

For each of our last five fiscal years and
prior thereto, we have incurred annual operating losses. We expect this trend to continue until such time that we can sell a sufficient
number of systems and achieve a cost structure to become profitable. We may not have adequate cash resources to reach the point
of profitability, and we may never become profitable. Even if we do achieve profitability, we may be unable to increase our sales
and sustain or increase our profitability in the future.

We experience significant fluctuations
in revenues from quarter to quarter due to a preponderance of one-time sales.

We have low volume, high dollar sales for
projects that are generally non-recurring, and therefore our sales have fluctuated significantly from period to period. For example,
when compared to the previous quarter, our revenues in 2010 decreased during the first, second and fourth quarters and increased
during the third quarter. In 2011, our revenue decreased during the first and fourth quarters and increased during the second and
third quarters. In 2012, our revenues increased during the first, second and fourth quarters and decreased during the third quarter.
In 2013, our revenues increased in the first, third and fourth quarters and decreased in the second quarter. Fluctuations cannot
be predicted because they are affected by the purchasing decisions and timing requirements of our customers, which are unpredictable.

We may be unable to fund our future
operating requirements, which could force us to curtail our operations.

To the extent that our funds are insufficient
to fund our future operating requirements, we would need to raise additional funds through further public or private equity or
debt financings depending upon prevailing market conditions. These financings may not be available to us, or if available, may
be on terms that are not favorable to us and could result in significant dilution to our stockholders and reduction of the trading
price of our stock (if then publicly traded). The state of worldwide capital markets could also impede our ability to raise additional
capital on favorable terms or at all. If adequate capital were not available to us, we likely would be required to significantly
curtail our operations or possibly even cease our operations.

We believe that our existing resources,
including cash and cash equivalents, future cash flows from operations and the expected net proceeds from this offering are sufficient
to meet the working capital requirements of our existing business for at least the next twelve months. After that our cash requirements
may increase.

7

If we experience a period of significant
growth or expansion, it could place a substantial strain on our resources.

If our cogeneration and chiller
products penetrate the market rapidly, we would be required to deliver even larger volumes of technically complex products or components
to our customers on a timely basis and at a reasonable costs to us. We have never ramped up our manufacturing capabilities to meet
large-scale production requirements. If we were to commit to deliver large volumes of products, we may not be able to satisfy these
commitments on a timely and cost-effective basis.

The execution of our growth strategy
is dependent upon the continued availability of third-party financing arrangements for our customers and is affected by general
economic conditions.

The recent recession, current unstable economic
conditions and limited availability of credit and liquidity could materially and adversely affect our business and results of operations
because purchasers of our systems often require third party financing. Purchasers may be unable or unwilling to finance the cost
to purchase our products or may be forced to cancel previously submitted orders or delay taking shipment until suitable credit
is again available. Collecting payment from customers facing liquidity challenges is also difficult.

We are dependent on a limited number
of third-party suppliers for the supply of key components for our products.

We use third-party suppliers for components
in many of our products. Our engine supplier is GM. Our generator supplier for our cogeneration products, other than the InVerde,
is Marathon Electric. To produce air conditioning, our engines drive a compressor purchased from J&E Hall International. The
loss of one of our suppliers could materially and adversely affect our business, if we are unable to replace them. While alternate
suppliers for the manufacture of our engine, generator and compressor have been identified, should the need arise, there can be
no assurance that alternate suppliers will be available and able to manufacture our engine, generator or compressor on acceptable
terms.

From time to time, shipments can be delayed
because of industry-wide or other shortages of necessary materials and components from third-party suppliers. A supplier's failure
to supply components in a timely manner, or to supply components that meet our quality, quantity, or cost requirements, or our
inability to obtain substitute sources of these components on a timely basis or on terms acceptable to us, could impair our ability
to deliver our products in accordance with contractual obligations.

We expect significant competition
for our products and services.

Many of our competitors and potential competitors are well established and have substantially greater financial, research and
development, technical, manufacturing and marketing resources than we do. If these larger competitors decide to focus on the development
of distributed power or cogeneration, they have the manufacturing, marketing and sales capabilities to complete research, development
and commercialization of these products more quickly and effectively than we can. There can also be no assurance that current
and future competitors will not develop new or enhanced technologies or more cost-effective systems, and therefore, there can
be no assurance that we will be successful in this competitive environment.

The Executive Order to accelerate
investments in industrial energy efficiency may lead to increased competition.

An Executive Order to accelerate investments
in industrial energy efficiency, including CHP, was promulgated in August 2012. The goal of the Executive Order is to supply 40
gigawatts of energy by 2020 from greater efficiency sources such as CHP systems. With this Executive Order, it is expected that
a number of barriers to CHP development will be removed with effective programs, policies, and financing opportunities resulting
in significant new capital investment in CHP. This initiative by the U.S. government may lead to increased competition in the CHP
market.

8

If we are unable to maintain our technological
expertise in design and manufacturing processes, we will not be able to successfully compete.

We believe that our future success will
depend upon our ability to continue to develop and provide innovative products and product enhancements that meet the increasingly
sophisticated needs of our customers.

However, this requires that we successfully
anticipate and respond to technological changes in design and manufacturing processes in a cost-effective and timely manner. The
development of new, technologically advanced products and enhancements is a complex and uncertain process requiring high levels
of innovation, as well as the accurate anticipation of technological and market trends. There can be no assurance that we will
successfully identify new product opportunities, develop and bring new or enhanced products to market in a timely manner, successfully
lower costs, and achieve market acceptance of our products, or that products and technologies developed by others will not render
our products or technologies obsolete or noncompetitive.

The introduction of products embodying new
technologies, and the shifting of customer demands or changing industry standards, could render our existing products obsolete
and unmarketable. We may experience delays in releasing new products and product enhancements in the future. Material delays in
introducing new products or product enhancements may cause customers to forego purchases of our products and purchase those of
our competitors.

Our intellectual property may not
be adequately protected.

We seek to protect our intellectual property
rights through patents, trademarks, copyrights, trade secret laws, confidentiality agreements, and licensing arrangements, but
we cannot ensure that we will be able to adequately protect our technology from misappropriation or infringement. We cannot ensure
that our existing intellectual property rights will not be invalidated, circumvented, challenged, or rendered unenforceable.

We have applied for and obtained patents
on certain key components used in our products. Specifically, the Company holds three patents, all of which are utilized in our
products. The first patent, from 2007, protects the incorporation of an inverter into an engine-driven CHP module and applies to
our InVerde model. The second patent, also from 2007, pertains to algorithms used for combustion control in our engines.
Our third patent, issued October 2013 in the United States, is for our Ultra low-emissions technology. This Ultra
technology applies to all of our gas engine-driven products and may have licensing application to other natural gas engines. In
addition, we have rights to a 2006 University of Wisconsin patent enabling us to use that patent’s microgrid control algorithms
for our specific use: engine-based power generation fueled by natural gas and diesel for engines less than 500 kW in electric power
output.

We have also filed for patents for
our Ultra low-emissions technology in Europe, Australia, Brazil, Canada, China, Costa Rica, the Dominican Republic, India,
Israel, Japan, Mexico, New Zealand, Nicaragua, Republic of Korea, Singapore, and South Africa. As discussed under Recent Developments,
the U.S. PTO has issued our patent. There is no assurance, however, that the Ultra low-emissions patent applications will
be approved in any other countries.

Our competitors may successfully challenge
the validity of our patents, design non-infringing products, or deliberately infringe our patents. There can be no assurance that
other companies are not investigating or developing other similar technologies. In addition, our intellectual property rights may
not provide a competitive advantage to us or ensure that our products and technology will be adequately covered by our patents
and other intellectual property. Any of these factors or the expiration, termination, or invalidity of one or more of our patents
may have a material adverse effect on our business.

Our control software is protected by
copyright laws or under an exclusive license agreement. Further, we rely on treatment of our technology as trade secrets through
confidentiality agreements, which our employees and vendors are required to sign. We also rely on non-disclosure agreements with
others that have or may have access to confidential information to protect our trade secrets and proprietary knowledge. These agreements
may be breached, and we may not have adequate remedies for any breach. Our trade secrets may also be or become known without breach
of these agreements or may be independently developed by competitors. Failure to maintain the proprietary nature of our technology
and information could harm our results of operations and financial condition.

We may be subject to infringement claims
in the future. The defense of any claims of infringement made against us by third parties could involve significant legal costs
and require our management to divert time from our business operations. If we are unsuccessful in defending any claims of infringement,
we may be forced to obtain licenses or to pay additional royalties to continue to use our technology. We may not be able to obtain
any necessary licenses on commercially reasonable terms or at all. If we fail to obtain necessary licenses or other rights, or
if these licenses are costly, our operating results would suffer either from reductions in revenues through our inability to serve
customers or from increases in costs to license third-party technologies.

Our success is dependent upon attracting
and retaining highly qualified personnel and the loss of key personnel could significantly hurt our business.

To achieve success, we must attract and
retain highly qualified technical, operational and executive employees. The loss of the services of key employees or an inability
to attract, train and retain qualified and skilled employees, specifically engineering, operations, and business development personnel,
could result in the loss of business or could otherwise negatively impact our ability to operate and grow our business successfully.

Our business is subject to product
liability and warranty claims.

Our business exposes us to potential product
liability claims, which are inherent in the manufacturing, marketing and sale of our products, and we may face substantial liability
for damages resulting from the faulty design or manufacture of products or improper use of products by end users. We currently
maintain a moderate level of product liability insurance, but there can be no assurance that this insurance will provide sufficient
coverage in the event of a claim. Also, we cannot predict whether we will be able to maintain such coverage on acceptable terms,
if at all, or that a product liability claim would not harm our business or financial condition. In addition, negative publicity
in connection with the faulty design or manufacture of our products would adversely affect our ability to market and sell our products.

We sell our products with warranties. There
can be no assurance that the provision in our financial statements for estimated product warranty expense will be sufficient. We
cannot ensure that our efforts to reduce our risk through warranty disclaimers will effectively limit our liability. Any significant
occurrence of warranty expense in excess of estimates could have a material adverse effect on our operating results, financial
condition and cash flow. Further, we have at times undertaken programs to enhance the performance of units previously sold. These
enhancements have at times been provided at no cost or below our cost. If we choose to offer such programs again in the future,
such actions could result in significant costs.

Certain businesses and consumers might
not consider cogeneration solutions as a means for obtaining their electricity and power needs.

Generating electricity and heat at the customers’
building (on-site CHP) is an established technology, but it is more complex than buying electricity from the utility and using
a furnace for heat. Customers have been slow to accept on-site CHP in part because of this complexity. In addition, the development
of a larger market for our products will be impacted by many factors that are out of our control, including cost competitiveness,
regulatory requirements, and the emergence of newer and potentially better technologies and products. If a larger market for cogeneration
technology in general and our products in particular fails to grow substantially, we may be unable to continue our business.

10

We operate in a highly regulated business
environment, and changes in regulation could impose significant costs on us or could make our products less economical, thereby
affecting demand for our products.

Several kinds of government regulations
– at federal, state, and local levels and in other countries affect our current and future business (see “Government
Regulation and Its Effect on Our Business” in the “Business” section of this prospectus. Our products must comply
with various local building codes and must undergo inspection by local authorities. Our products are also certified by a third
party to conform to specific standards. These certifications require continuous verification by a company that monitors our processes
and design every three months. Our InVerde product is also certified to Europe’s standard CE mark (European Conformity),
which is mandatory for products imported into the European Union for commercial sale. If our products ceased to meet the criteria
necessary for the applicable certifications, we may lose the ability to sell our products in certain jurisdictions, which may materially
and adversely affect our business.

Regulatory agencies may further impose special
requirements for the implementation and operation of our products that could significantly affect or even eliminate some of our
target markets. We also may incur material costs or liabilities in complying with future government regulations. Furthermore, our
potential utility customers must themselves comply with numerous laws and regulations, which may be complicated by further deregulation
of the utility industry. We cannot determine how such deregulation may ultimately affect the market for our products. Changes in
regulatory standards or policies could reduce the level of investment in the research and development of alternative power sources,
including our products. Any reduction or termination of such programs could increase the cost to our potential customers, making
our systems less desirable and thereby adversely affect our business and financial condition.

Utilities or governmental entities
could hinder our entry into and growth in the marketplace, and we may not be able to effectively sell our products.

Utilities or governmental entities on occasion
have placed barriers to the installation of our products or their interconnection with the electric grid, and they may continue
to do so. Utilities may charge additional fees to customers who install on-site CHP and rely on the grid for back-up power. These
types of restrictions, fees, or charges could make it harder for customers to install our products or use them effectively, as
well as increasing the cost to our potential customers. This could make our systems less desirable, thereby adversely affecting
our revenue and other operating results.

We may not achieve production cost
reductions necessary to competitively price our products, which would adversely affect our sales.

We believe that we will need to reduce the
unit production cost of our products over time to maintain our ability to offer competitively priced products. Our ability to achieve
cost reductions will depend on our ability to develop low-cost design enhancements, to obtain necessary tooling and favorable supplier
contracts, and to increase sales volumes so we can achieve economies of scale. We cannot assure you that we will be able to achieve
any such production cost reductions. Our failure to do so could have a material adverse effect on our business and results of operations.

Our products contain a number of commodity
materials, from metals, which include steel, special high temperature alloys, copper, nickel and molybdenum, to computer components.
The availability of these commodities could impact our ability to acquire the materials necessary to meet our requirements. The
cost of metals has historically fluctuated. The pricing could impact the costs to manufacture our products. If we are not able
to acquire commodity materials at prices and on terms satisfactory to us or at all, our operating results may be materially adversely
affected.

11

Our products involve a lengthy sales
cycle and we may not anticipate sales levels appropriately, which could impair our results of operations.

The sale of our products typically involves
a significant commitment of capital by customers, with the attendant delays frequently associated with large capital expenditures.
For these and other reasons, the sales cycle associated with our products is typically lengthy and subject to a number of significant
risks over which we have little or no control. We expect to plan our production and inventory levels based on internal forecasts
of customer demand, which is highly unpredictable and can fluctuate substantially. If sales in any period fall significantly below
anticipated levels, our financial condition, results of operations and cash flow would suffer. If demand in any period increases
well above anticipated levels, we may have difficulties in responding, incur greater costs to respond, or be unable to fulfill
the demand in sufficient time to retain the order, which would negatively impact our operations. In addition, our operating expenses
are based on anticipated sales levels, and a high percentage of our expenses are generally fixed in the short term. As a result
of these factors, a small fluctuation in timing of sales can cause operating results to vary materially from period to period.

The economic viability of our projects
depends on the price spread between fuel and electricity, and the variability of these prices creates a risk that our projects
will not be economically viable and that potential customers will avoid such energy price risks.

The economic viability of our CHP products
depends on the spread between natural gas fuel and electricity prices. Volatility in one component of the spread, such as the cost
of natural gas and other fuels (e.g., propane or distillate oil), can be managed to some extent by means of futures contracts.
However, the regional rates charged for both base load and peak electricity may decline periodically due to excess generating capacity
or general economic recessions.

Our products could become less competitive
if electric rates were to fall substantially in the future. Also, potential customers may perceive the unpredictable swings in
natural gas and electricity prices as an increased risk of investing in on-site CHP, and may decide not to purchase CHP products.

We are exposed to credit risks with
respect to some of our customers.

To the extent our customers do not advance
us sufficient funds to finance our costs during the execution phase of our contracts, we are exposed to the risk that they will
be unable to accept delivery or that they will be unable to make payment at the time of delivery.

We may make acquisitions that could
harm our financial performance.

To expedite development of
our corporate infrastructure, particularly with regard to equipment installation and service functions, we anticipate the future
acquisition of complementary businesses. Risks associated with such acquisitions include the disruption of our existing operations,
loss of key personnel in the acquired companies, dilution through the issuance of additional securities, assumptions of existing
liabilities, and commitment to further operating expenses. If any or all of these problems actually occur, acquisitions could negatively
impact our financial performance and future stock value.

Our ability to access capital for
the repayment of debts and for future growth may be limited due to periods of fluctuating financial markets and periods of economic
disruption and recession. We may be affected by unknown future market conditions.

Our ability to continue to access capital
could be impacted by various factors including general market conditions and the continuing slowdown in the economy, interest rates,
the perception of our potential future earnings and cash distributions, any unwillingness on the part of lenders to make loans
to us, and any deterioration in the financial position of lenders that might make them unable to meet their obligations to us.

Our business is affected by general
economic conditions and related uncertainties affecting the markets in which we operate. Potential future economic conditions,
including an unstable global economy, could adversely impact our business in 2014 and beyond.

The current unstable economic conditions
could adversely impact our business in 2014 and beyond, resulting in reduced demand for our products, increased rate of order cancellations
or delays, increased risk of supplier bankruptcy, increased rate of supply order cancellation or delays, increased risk of excess
and obsolete inventories, increased pressure on the prices for our products and services; and greater difficulty in collecting
accounts receivable.

12

Risks Related to this offering and ownership of our common
stock

No public market for our common stock
currently exists, and an active trading market for our common stock may not develop or be sustained following this offering.

Prior to this offering, there has been
no public market for our common stock. The public offering price for our common stock will be determined through negotiations between
us and the investors in this offering. This price will not necessarily reflect the price at which investors in the market will
be willing to buy and sell our common stock following this offering. Although we will not consummate this offering unless our common
stock is approved for listing on The NASDAQ Capital Market, an active trading market for our shares may never develop or, if developed,
be maintained following this offering. If an active market for our common stock does not develop or is not maintained, it may be
difficult for you to sell shares you purchase in this offering without depressing the market price for the shares or at all. An
inactive trading market may also impair our ability to raise capital to continue to fund operations by selling shares and may impair
our ability to acquire other companies or technologies by using our shares as consideration.

Our failure to meet the continued
listing requirements of The NASDAQ Capital Market could result in a de-listing of our common stock.

If after listing we fail to satisfy
the continued listing requirements of The NASDAQ Capital Market, such as the corporate governance requirements or the minimum closing
bid price requirement, NASDAQ may take steps to de-list our common stock. Such a de-listing would likely have a negative effect
on the price of our common stock and would impair your ability to sell or purchase our common stock when you wish to do so. In
the event of a de-listing, we would take actions to restore our compliance with NASDAQ’s listing requirements, but we can
provide no assurance that any such action taken by us would allow our common stock to become listed again, stabilize the market
price or improve the liquidity of our common stock, prevent our common stock from dropping below the NASDAQ minimum bid price requirement
or prevent future non-compliance with NASDAQ’s listing requirements.

If securities or industry analysts
do not publish research or publish inaccurate or unfavorable research about our business, our share price and trading volume could
decline.

The trading market for our common stock
will depend on the research and reports that securities or industry analysts publish about us or our business. We do not have any
control over these analysts. There can be no assurance that analysts will cover us, or provide favorable coverage. If one or more
analysts downgrade our stock or change their opinion of our stock, our share price would likely decline. In addition, if one or
more analysts cease coverage of our company or fail to regularly publish reports on us, we could lose visibility in the financial
markets, which could cause our share price or trading volume to decline.

Investment in our common stock is
subject to price fluctuations and market volatility.

Historically, valuations of many small companies
have been highly volatile. The securities of many small companies have experienced significant price and trading volume fluctuations,
unrelated to the operating performance or the prospects of such companies. The public offering price for our shares will be determined
by negotiations between us and the investors in the offering and may not be indicative of prices that will prevail in the trading
market. The market price of shares of our common stock could be subject to wide fluctuations in response to many risk factors listed
in this section, and others beyond our control, including:

disputes or other developments related to proprietary rights, including patents, litigation matters, and our ability to obtain,
maintain, defend or enforce proprietary rights relating to our products and technologies;

•

announcement or expectation of additional financing efforts;

•

sales of our common stock by us, our insiders, or our other stockholders; and

•

general economic and market conditions.

Furthermore, the stock markets have experienced
extreme price and volume fluctuations that have affected and continue to affect the market prices of equity securities of many
companies. These fluctuations often have been unrelated or disproportionate to the operating performance of those companies. These
broad market and industry fluctuations, as well as general economic, political, and market conditions such as recessions, interest
rate changes, or international currency fluctuations, may negatively impact the market price of shares of our common stock. In
addition, such fluctuations could subject us to securities class action litigation, which could result in substantial costs and
divert our management’s attention from other business concerns, which could potentially harm our business. If the market
price of shares of our common stock after this offering does not exceed the public offering price, you may not realize any return
on your investment in us and may lose some or all of your investment.

Purchasers in this offering will experience
immediate and substantial dilution in the book value of their investment.

The public offering price of the
shares offered by this prospectus will be substantially higher than the pro forma as adjusted net tangible book value per
share of our common stock based on the total value of our tangible assets less our total liabilities immediately following
this offering. Therefore, if you purchase shares of our common stock in this offering, you will experience immediate and
substantial dilution of approximately $4.35 per share in the price you pay for shares of our common stock as compared to the
as adjusted net tangible book value per share, based on an assumed public offering price of $5.25 per share, the midpoint of
the price range set forth on the cover page of this prospectus. To the extent outstanding options to purchase shares of
Common Stock are exercised, there will be further dilution. Investors who purchase shares in this offering will contribute a
substantial portion of the equity capital raised by us through the date of this offering, but will own a significantly lower
percentage of the shares outstanding immediately following the completion of this offering. For further information on this
calculation, see the “Dilution” section of this prospectus.

We could issue additional Common Stock,
which might dilute the book value of our common stock.

Our board of directors has the authority,
without action or vote of our stockholders, to issue all or a part of any authorized but unissued shares. Such stock issuances
may be made at a price that reflects a discount from the then-current trading price of our common stock. We may issue securities
that are convertible into or exercisable for a significant amount of our common stock. These issuances would dilute the percentage
ownership interest of holders of our securities, which would have the effect of reducing their influence on matters on which our
stockholders vote, and might dilute the book value of our common stock. Investors in our securities may incur additional dilution
of net tangible book value if holders of stock options, whether currently outstanding or subsequently granted, exercise their options
or if warrant holders exercise their warrants to purchase shares of our common stock. There can be no assurance that any future
offering will be consummated or, if consummated, will be at a share price equal or superior to the price paid by our investors
even if we meet our technological and marketing goals.

14

We may be subject to securities litigation,
which is expensive and could divert management attention.

Our share price may be volatile, and in
the past companies that have experienced volatility in the market price of their stock have been subject to an increased incidence
of securities class action litigation. We may be the target of this type of litigation in the future. Securities litigation against
us could result in substantial costs and divert our management’s attention from other business concerns, which could seriously
harm our business.

Our quarterly operating results are
subject to fluctuations, and if we fail to meet the expectations of securities analysts or investors, our share price may decrease
significantly.

Our annual and quarterly results may vary
significantly depending on various factors, many of which are beyond our control. If our earnings do not meet the expectations
of securities analysts or investors, the price of our stock could decline. Also, because our sales are primarily made on a purchase
order basis, customers may generally cancel, reduce or postpone orders, resulting in reductions to our net sales and profitability.

Future sales of Common Stock by our
existing stockholders may cause our stock price to fall.

The market price of our common stock could
decline as a result of sales by our stockholders of shares of Common Stock in the market or the perception that these sales could
occur. As a result, such sales could significantly impact the trading price of our common stock and the ability of other stockholders
to sell shares of our common stock. These sales might also make it more difficult for us to sell equity securities at a time and
price that we deem appropriate and thus inhibit our ability to raise additional capital when it is needed.

Because we do not intend to pay cash
dividends, our stockholders will receive no current income from holding our stock.

We have paid no cash dividends on our capital
stock to date and we currently intend to retain all of our future earnings, if any, to fund the development and growth of our business.
In addition, the terms of any future debt or credit facility may preclude us from paying these dividends. As a result, capital
appreciation, if any, of our common stock will be the sole source of gain for our stockholders for the foreseeable future.

We are controlled by a small group
of majority stockholders, and our minority stockholders will be unable to effect changes in our governance structure or implement
actions that require stockholder approval, such as a sale of the Company.

George N. Hatsopoulos and John N. Hatsopoulos,
who are brothers, beneficially own approximately 48.0% of our outstanding shares of Common Stock. These stockholders have the ability
to control various corporate decisions, including our direction and policies, the election of directors, the content of our charter
and bylaws and the outcome of any other matter requiring stockholder approval, including a merger, consolidation and sale of substantially
all of our assets or other change of control transaction. The concurrence of our minority stockholders will not be required for
any of these decisions. This concentration of voting power could delay or prevent an acquisition of us on terms that other stockholders
may desire. The interests of this group of stockholders may not always coincide with your interests or the interests of other stockholders
and they may act in a manner that advances their best interests and not necessarily those of other stockholders, including seeking
a premium value for their Common Stock, which might affect the prevailing market price for our common stock.

15

We are controlled by our two founding
stockholders, George N. Hatsopoulos and John N. Hatsopoulos. These stockholders have registered the majority of their holdings
for resale and therefore are able to sell all of their Common Stock.

John N. Hatsopoulos and George N. Hatsopoulos
have registered the majority of their holdings of our common stock for resale primarily for estate planning purposes. For that
reason, the timing and the amount of any future sales by them is difficult to predict. George Hatsopoulos is a director but not
an officer of the Company. John Hatsopoulos is the Chief Executive Officer and a key employee of the Company. If John Hatsopoulos
or George Hatsopoulos were to sell a substantial portion of their shares in the Company, they would no longer have a substantial
continuing interest in the Company. If that were to occur, it may have a material adverse effect on their performance as director
or Chief Executive Officer, as applicable, and on the business of the Company. Further, substantial sales of their Common Stock
may result in a decline in the market price of our common stock. The Company’s securities held by each of John Hatsopoulos
and George Hatsopoulos will be subject to 180-day lock-up periods pursuant to the lock-up agreements described in the “Plan
of Distribution” section of this prospectus.

We have broad discretion in the use
of net proceeds from this offering and may not use them effectively.

Our management will have broad discretion
in the application of the net proceeds from this offering, including for any of the purposes described in the section entitled
“Use of Proceeds,” and you will not have the opportunity as part of your investment decision to assess whether the
net proceeds are being used appropriately. Because of the number and variability of factors that will determine our use of the
net proceeds from this offering, their ultimate use may vary substantially from their intended use. The failure by our management
to apply these funds effectively could harm our business. Pending their use, we may invest the net proceeds from this offering
in short-term, investment-grade, interest-bearing securities. These investments may not yield a favorable return to our stockholders.
Further, we anticipate that a certain portion of the proceeds from this offering will be used to finance Ilios, an entity of which
we own only 65.0%. As such, your investment in our common stock may result in benefits of which you may only experience a portion.

There has been a material weakness
in our disclosure controls and procedures and our internal control over financial reporting, which could harm our operating results
or cause us to fail to meet our reporting obligations.

As of our fiscal year end, December 31,
2013, our principal executive officer and principal accounting officer performed an evaluation of controls and procedures and concluded
that our controls were not effective to provide reasonable assurance that information required to be disclosed by our Company in
reports that we file under the Exchange Act, is recorded, processed, summarized and reported as when required. Management conducted
an evaluation of our internal control over financial reporting and based on this evaluation, management concluded that the company’s
internal control over financial reporting was not effective as of December 31, 2013. The Company currently does not have personnel
with a sufficient level of accounting knowledge, experience and training in the selection, application and implementation of generally
acceptable accounting principles as it relates to complex transactions and financial reporting requirements. The Company also has
a small number of employees dealing with general controls over information technology security and user access. This constitutes
a material weakness in financial reporting. Any failure to implement effective internal controls could harm our operating results
or cause us to fail to meet our reporting obligations. Inadequate internal controls could also cause investors to lose confidence
in our reported financial information, which could have a negative effect on the trading price of our common stock, and may require
us to incur additional costs to improve our internal control system.

16

Trading of our common stock may be
restricted by the SEC’s “penny stock” regulations which may limit a stockholder’s ability to buy and sell
our stock.

The SEC has adopted regulations that generally
define “penny stock” to be any equity security that has a market price less than $5.00 per share or an exercise price
of less than $5.00 per share, subject to certain exceptions. Our securities may be covered by the penny stock rules, which impose
additional sales practice requirements on broker-dealers who sell to persons other than established customers and accredited investors.
The penny stock rules require a broker-dealer, prior to a transaction in a penny stock not otherwise exempt from the rules, to
deliver a standardized risk disclosure document in a form prepared by the SEC that provides information about penny stocks and
the nature and level of risks in the penny stock market. The broker-dealer also must provide the customer with current bid and
other quotations for the penny stock, the compensation of the broker-dealer and its salesperson in the transaction and monthly
account statement showing the market value of each penny stock held in the customer’s account. The bid and offer quotations,
and the broker-dealer and salesperson compensation information, must be given to the customer orally or in writing prior to effecting
the transaction and must be given to the customer in writing before or with the customer’s confirmation. In addition, the
penny stock rules require that prior to a transaction in a penny stock not otherwise exempt from these rules, the broker-dealer
must make a special written determination that the penny stock is a suitable investment for the purchaser and receive the purchaser’s
written agreement to the transaction. These disclosure and suitability requirements may have the effect of reducing the level of
trading activity in the secondary market for a stock that is subject to these penny stock rules. Consequently, these penny stock
rules may affect the ability of broker-dealers to trade our securities. We believe that the penny stock rules may discourage investor
interest in and limit the marketability of our capital stock. Trading of our capital stock may be restricted by the SEC’s
“penny stock” regulations which may limit a stockholder’s ability to buy and sell our stock.

The JOBS Act allows us to postpone
the date by which we must comply with certain laws and regulations and reduces the amount of information provided by us in reports
filed with the SEC. We cannot be certain if the reduced disclosure requirements applicable to emerging growth companies will make
our common stock less attractive to investors.

We are and we will remain an “emerging
growth company”, as defined in the Jumpstart Our Business Startups Act of 2012, or the JOBS Act, until the earliest to occur
of (i) the last day of the fiscal year during which our total annual gross revenues equal or exceed $1 billion (subject to adjustment
for inflation), (ii) the last day of the fiscal year following the fifth anniversary of our initial public offering, (iii) the
date on which we have, during the previous three-year period, issued more than $1 billion in non-convertible debt, or (iv) the
date on which we are deemed a large accelerated filer under the Exchange Act.

For so long as we remain an emerging growth
company we are not required to:

•

have an auditor report on our internal controls over financial reporting pursuant to Section 404(b) of the Sarbanes-Oxley Act;

•

comply with any requirement that may be adopted by the Public Company Accounting Oversight Board regarding mandatory audit
firm rotation or a supplement to the auditor’s report providing additional information about the audit and the financial
statements (i.e., an auditor discussion and analysis);

disclose certain executive compensation related items such as the correlation between executive compensation and financial
performance and comparisons of the Chief Executive Officer’s compensation to median employee compensation, when such disclosure
requirements are adopted.

17

In addition, Section 107 of the JOBS Act
also provides that an emerging growth company can take advantage of the extended transition period provided in Section 7(a)(2)(B)
of the Securities Act of 1933, as amended, or the Securities Act, for complying with new or revised accounting standards. An emerging
growth company can therefore delay the adoption of certain accounting standards until those standards would otherwise apply to
private companies. However, we have chosen to “opt out” of such extended transition period, and as a result, we will
comply with new or revised accounting standards on the relevant dates on which adoption of such standards is required for non-emerging
growth companies. Section 107 of the JOBS Act provides that our decision to opt out of the extended transition period for complying
with new or revised accounting standards is irrevocable.

We cannot predict if investors will find
our common stock less attractive because we may rely on some of these exemptions. If some investors find our common stock less
attractive as a result, there may be a less active trading market for our common stock and our stock price may be more volatile.
If we avail ourselves of certain exemptions from various reporting requirements, our reduced disclosure may make it more difficult
for investors and securities analysts to evaluate us and may result in less investor confidence.

We will incur significantly increased
costs and devote substantial management time as a result of operating as a public company particularly after we are no longer an
“emerging growth company.”

As a public company, we will incur
significant legal, accounting and other expenses that we did not incur as a private company. For example, we will be required to
comply with certain of the requirements of the Sarbanes-Oxley Act and the Dodd-Frank Wall Street Reform and Consumer Protection
Act, as well as rules and regulations subsequently implemented by the SEC, and The NASDAQ Capital Market, our anticipated stock
exchange, including the establishment and maintenance of effective disclosure and financial controls and changes in corporate governance
practices. We expect that compliance with these requirements will increase our legal and financial compliance costs and will make
some activities more time consuming and costly. In addition, we expect that our management and other personnel will need to divert
attention from operational and other business matters to devote substantial time to these public company requirements. In particular,
we expect to incur significant expenses and devote substantial management effort toward ensuring compliance with the requirements
of Section 404 of the Sarbanes-Oxley Act.

As noted above, for as long as we remain
an “emerging growth company” as defined in the JOBS Act, we intend to take advantage of certain exemptions from various
reporting requirements that are applicable to other public companies that are not “emerging growth companies.” However,
after we are no longer an “emerging growth company,” we expect to incur additional management time and cost to comply
with the more stringent reporting requirements applicable to companies that are deemed accelerated filers or large accelerated
filers, including complying with the auditor attestation requirements of Section 404 of the Sarbanes-Oxley Act. We cannot predict
or estimate the amount of additional costs we may incur as a result of becoming a public company or the timing of such costs.

our ability to effectively manage our growth and successfully enter new markets; and

•

the attraction and retention of qualified employees and key personnel.

We may not actually achieve the plans,
intentions, or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking
statements. Actual results or events could differ materially from the plans, intentions, and expectations disclosed in the forward-looking
statements we make. We have included important factors in the cautionary statements included in this prospectus, particularly in
the “Risk Factors” section, that we believe could cause actual results or events to differ materially from the forward-looking
statements that we make. Our forward-looking statements do not reflect the potential impact of any future acquisitions, mergers,
dispositions, joint ventures, or investments we may make.

You should read this prospectus and
the documents that we reference in this prospectus and have filed as exhibits to the registration statement of which this prospectus
is a part completely and with the understanding that our actual future results may be materially different from what we expect.
The forward-looking statements contained in this prospectus are made as of the date of this prospectus, and we do not assume any
obligation to update any forward-looking statements except as required by applicable law.

19

USE OF PROCEEDS

We estimate that we will receive net
proceeds of approximately $9.3 million from the sale of our common stock in this offering, after deducting the estimated placement
agent fees and estimated offering expenses payable by us. A $0.25 increase (decrease) in the assumed public offering price of
$5.25 per share would increases (decrease) the net proceeds of this offering by approximately $466,000, assuming that the number
of shares we are offering, as set forth on the cover page of this prospectus, remains the same, after deducting the estimated
placement agent fees and estimated offering expenses payable by us. We may also increase or decrease the number of shares we are
offering. Each increase (decrease) of 100,000 shares in the number of shares we are offering would increase (decrease) the net
proceeds to us from this offering by approximately $500,000, assuming that the assumed public offering price remains the same,
and after deducting the estimated placement agent fees and estimated offering expenses payable by us.

We currently expect to use the net
proceeds from this offering to:

•

Expand our turnkey design and installation contracting services business in our core markets in the Northeast United States
and California. Proceeds will be used for additional sales and technical staff to support the business and for working capital
to complete these projects. We anticipate expanding our service and turnkey operations to new territories, which will likewise
require startup capital.

•

Further expand our business into foreign markets.

•

Expand our low-emissions technology business to other markets, including applying our emissions technology to non-Tecogen engines
in a wider range of industrial markets.

•

Refine our existing models and develop new products, including additional CHP and Ilios heat pump products that will use the
advanced engine developed under completed research contract with the California Energy Commission (see “R&D Capabilities”
below).

The remainder of the net proceeds from
this offering may be used for working capital and general corporate purposes.

If we receive substantially less than
the maximum proceeds from this offering, we believe that we will have access to other funding sources that, together with the proceeds
we do receive, will be sufficient to meet our working capital requirements for at least the next twelve months.

The actual amount we spend for such
purposes will depend on then-existing conditions, including our financial condition, operating results, business prospects, and
other factors that we may deem relevant. Accordingly, our management will have significant flexibility in applying the net proceeds
of this offering. Pending our use of the net proceeds from this offering, we intend to invest the net proceeds in a variety of
capital preservation investments, including short-term, investment-grade, interest-bearing instruments, and U.S. government securities.

We have no current understandings,
commitments or agreements with respect to any material acquisition of or investment in any technologies, products, or companies.

DIVIDENDS

To date, we have not declared or paid
any dividends on our outstanding shares. We currently do not anticipate paying any cash dividends in the foreseeable future on
our common stock. Although we intend to retain our earnings to finance our operations and future growth, our Board of Directors
will have discretion to declare and pay dividends in the future. Payment of dividends in the future will depend upon our earnings,
capital requirements and other factors, which our Board of Directors may deem relevant.

20

DETERMINATION OF OFFERING PRICE

The offering price for the shares in
this offering was determined by us after negotiation with the investors in this offering. In determining the offering price of
the shares we considered several factors including the following:

•

our status of business development;

•

our new business structure and operations;

•

prevailing market conditions, including the history and prospects for our industry;

•

market valuations of other companies that we and the Placement Agent believe to be comparable to us;

•

our future prospects and the experience of our management;

•

our capital structure; and

•

other factors deemed relevant.

Therefore, the public offering price
of the shares does not necessarily bear any relationship to established valuation criteria and may not be indicative of prices
that may prevail at any time or from time to time in the public market for the Common Stock. You cannot be sure that a public market
for any of our securities will develop and continue or that the securities will ever trade at a price at or higher than the offering
price in this prospectus.

21

CAPITALIZATION

The following table sets forth our cash
and cash equivalents and our capitalization as of December 31, 2013:

•

on an actual basis;

•

on a pro forma basis to give effect to the private placement of 1,400 shares of common stock at $4.50 per share from January
1 to January 17, 2014, the exercise of 5,000 options at $1.20 on February 18, 2014 and the repayment of debt to the Company's CEO
on January 6, 2014 consisting of principal of $2,950,000 and accrued interest of $200,658; and

•

on a pro forma, as adjusted basis, to give effect to the assumed sale of 2,000,000 shares of our common stock in this offering
at an assumed public offering price of $5.25 per share, the midpoint of the price range set forth on the cover page of this prospectus,
after deducting estimated placement agent fees and estimated offering expenses payable by us.

You should read this table in conjunction
with the sections titled “Selected Consolidated Financial Data” and “Management’s Discussion and Analysis
of Financial Condition and Results of Operations” and our financial statements and related notes included elsewhere in this
prospectus.

Each $0.25 increase (decrease) in the assumed
public offering price of $5.25 per share (the midpoint of the price range set forth on the cover page of this prospectus) would
increase (decrease), respectively, the amount of cash, and cash equivalents and short-term investments, additional paid-in capital,
total stockholders’ equity (deficit) and total capitalization by approximately $466,000, assuming the number of shares
offered by us remains the same and after deducting the estimated underwriting discounts and commissions and estimated offering
expenses payable by us. We may also increase or decrease the number of shares we are offering. An increase (decrease) of 100,000
shares in the number of shares we are offering would increase (decrease), respectively, the amount of cash and cash equivalents,
additional paid-in capital, total stockholders’ equity (deficit) and total capitalization by approximately $490,000, assuming
the assumed public offering price remains the same. The pro forma as adjusted information is illustrative only, and we will adjust
this information based on the actual public offering price, number of shares offered and other terms of this offering determined
at pricing.

22

The above table is based on 15,155,200 shares
of our common stock outstanding as of December 31, 2013 and excludes as of that date the following:

•

1,148,000 shares of Common Stock issuable upon the exercise of stock options outstanding prior to this offering under our stock
incentive plan, at a weighted average exercise price of $2.13 per share;

•

58,683 shares of Common Stock available for future grants under our stock incentive plan;

•

555,556 shares of Common Stock issuable pursuant to convertible debentures with an outstanding principal amount of $3,000,000
and a conversion price of $5.40 per share.

23

DILUTION

Purchasers of the shares offered by
this prospectus will suffer immediate and substantial dilution in the net tangible book value per share of Common Stock. Our net
tangible book value as of December 31, 2013, was approximately $6,071,696, or $0.40 per share. Net tangible book value per
share is calculated by subtracting our total liabilities from our total tangible assets, which is total assets less intangible
assets, and dividing this amount by the number of shares of Common Stock outstanding.

Dilution in net tangible book value
per share represents the difference between the amount per share paid by purchasers in this offering and the as adjusted pro forma
net tangible book value per share of our common stock immediately after this offering. After giving effect to the sale by us of
all 2,000,000 shares offered in this offering at an assumed public offering price of $5.25 per share, the midpoint of the price
range set forth on the cover page of this prospectus, and after deducting estimated placement agent fees and estimated offering
expenses payable by us, our as adjusted net tangible book value as of December 31, 2013, would have been approximately $15,413,000,
or $ 0.90 per share. This represents an immediate increase in the net tangible book value of $0.50 per share to our existing stockholders
and an immediate dilution in net tangible book value of $4.35 per share to investors in this offering. The following table illustrates
this per share dilution:

Price per share to investors

$

5.25

Net tangible book value per share as of December 31, 2013

0.40

Increase in net tangible book value per share attributable to this offering

0.50

As adjusted net tangible book value per share as of December 31, 2013, after giving effect to this offering

0.90

Dilution in net tangible book value per share to investors

$

4.35

The above table is based on 15,155,200
shares of our common stock outstanding as of December 31, 2013 and excludes as of that date the following:

•

1,148,000 shares of Common Stock issuable upon the exercise of stock options outstanding prior to this offering under our stock
incentive plan, at a weighted average exercise price of $2.13 per share;

•

58,683 shares of Common Stock available for future grants under our stock incentive plan;

•

555,556 shares of Common Stock issuable pursuant to convertible debentures with an outstanding principal amount of $3,000,000
and a conversion price of $5.40 per share.

Each $0.25 increase (decrease) in the
assumed public offering price of $5.25 per share (the midpoint of the price range set forth on the cover page of this prospectus)
, would increase (decrease) our pro forma as adjusted net tangible book value by approximately $466,000, our as adjusted net
tangible book value per share by approximately $0.027 and dilution per share to new investors by approximately $0.22, assuming
the number of shares offered hereby remains the same. We may also increase or decrease the number of shares we are offering. A
100,000 share increase (decrease) in the number of shares of common stock offered by us would increase (decrease) our pro forma
as adjusted net tangible book value by approximately $490,000, our as adjusted net tangible book value per share by approximately
$0.02, and dilution per share to new investors would be approximately $4.33, assuming the public offering price remains the same.
The pro forma as adjusted information is illustrative only, and we will adjust this information based on the actual public offering
price, number of shares offered and other terms of this offering determined at pricing.

To the extent that any options are exercised,
new options are issued under our stock option or stock incentive plans, or we otherwise issue additional shares of Common Stock
in the future, there will be further dilution to new investors.

24

SELECTED CONSOLIDATED FINANCIAL DATA

The summary consolidated statements
of operations data for each of the years ended December 31, 2013 and 2012 and the summary consolidated balance sheet data as of
December 31, 2013 and 2012, have been derived from our audited consolidated financial statements that are included elsewhere
in this prospectus.

You should read this information together
with the consolidated financial statements and related notes and other information under “Management’s Discussion and
Analysis of Financial Condition and Results of Operations” included elsewhere in this prospectus.

Year Ended December 31,

Consolidated Statement of Operations Data:

2013

2012

Revenues

$

15,849,869

$

15,253,972

Cost of sales

10,819,741

9,388,898

Gross profit

5,030,128

5,865,074

Operating expenses

General and administrative

7,018,133

6,643,120

Selling

1,423,587

1,225,580

Aborted public offering costs

258,512

—

8,700,232

7,868,700

Loss from operations

(3,670,104

)

(2,003,626

)

Other income (expense)

Interest and other income

3,958

48,397

Interest expense

(141,065

)

(71,208

)

(137,107

)

(22,811

)

Loss before income taxes

(3,807,211

)

(2,026,437

)

Consolidated net loss

(3,807,211

)

(2,026,437

)

Less: Loss attributable to the noncontrolling interest

357,722

389,480

Net loss attributable to Tecogen Inc.

$

(3,449,489

)

$

(1,636,957

)

Net loss per share – basic and diluted

$

(0.26

)

$

(0.12

)

Weighted average shares outstanding – basic and diluted

13,385,155

13,135,071

As of December 31, 2012

As of December 31, 2013

Consolidated Balance Sheet Data:

Actual

Actual

Pro Forma(1)

Pro Forma As Adjusted(2)

Cash and cash equivalents

$

1,572,785

$

7,713,899

$

4,575,541

$

13,916,541

Short-term investments (restricted)

181,859

—

—

—

Working capital

4,078,704

5,565,789

5,578,089

14,919,089

Total assets

9,117,249

17,630,069

14,491,711

23,832,711

Total liabilities

4,334,214

10,564,176

7,814,834

7,814,834

Total stockholders’ equity

$

4,783,035

$

7,065,893

$

7,078,193

$

16,419,193

(1)

The pro forma consolidated balance sheet data in the table above gives effect to the private placement of 1,400 shares of common stock at $4.50 per share from January 1 to January 17, 2014, the exercise of 5,000 options at $1.20 on February 18, 2014 and the repayment of debt to the Company's CEO on January 6, 2014 consisting of principal of $2,950,000 and accrued interest of $200,658.

(2)

The pro forma as adjusted consolidated balance sheet data in the table above gives effect to our receipt of the estimated net
proceeds to us from this offering at an assumed public offering price of $5.25 per share, the midpoint of the price range set forth
on the cover page of this prospectus, after deducting estimated placement agent fees and estimated offering expenses payable by
us.

25

MANAGEMENT’S DISCUSSION AND ANALYSIS
OF

FINANCIAL CONDITION AND RESULTS OF OPERATIONS

Overview

Tecogen designs, manufactures and sells
industrial and commercial cogeneration systems that produce combinations of electricity, hot water, and air conditioning using
automotive engines that have been specially adapted to run on natural gas. Cogeneration systems are efficient because in addition
to supplying mechanical energy to power electric generators or compressors – displacing utility supplied electricity –
they provide an opportunity for the facility to incorporate the engine’s waste heat into onsite processes such as space and
potable water heating. We produce standardized, modular, small-scale products, with a limited number of product configurations
that are adaptable to multiple applications. We refer to these combined heat and power products as CHP (electricity plus heat)
and MCHP (mechanical power plus heat).

Our products are sold directly to end-users
by our in-house marketing team and by established sales agents and representatives. We have agreements in place with distributors
and sales representatives, including American DG Energy, which is an affiliated company. Our existing customers include hospitals
and nursing homes, colleges and universities, health clubs and spas, hotels and motels, office and retail buildings, food and beverage
processors, multi-unit residential buildings, laundries, ice rinks, swimming pools, factories, municipal buildings, and military
installations. We have an installed base of more than 2,100 units. Many of these have been operating for almost 25 years.

In 2009, we created a majority-owned subsidiary
Ilios to develop and distribute a line of ultra-high-efficiency heating products, including a high efficiency water heater. These
products provide twice the efficiency of conventional commercial and industrial boilers (based upon management estimates) utilizing
advanced thermodynamic principles. As of the date of this prospectus, we own a 65.0% interest in Ilios.

For each of our last five fiscal years and
prior thereto, we have incurred annual operating losses. We expect this trend to continue until such time that we can sell a sufficient
number of systems and achieve a cost structure to become profitable. We may not have adequate cash resources to reach the point
of profitability, and we may never become profitable. Even if we do achieve profitability, we may be unable to increase our sales
and sustain or increase our profitability in the future.

Although we may, from time to time, have
one or a few customers who may represent more than 10% of our product revenue for a given year, we are not dependent on the recurrence
of revenue from those customers. Our product revenue is such that customers may make a large purchase once and may not ever make
a purchase again. Our equipment is built to last 20 or more years, therefore, our product revenue model is not dependent on recurring
sales transactions from the same customer. Our service revenue, however, may lend itself to recurring revenue from particular customers;
although we currently do not have any service revenue customers who make up more than 10% of our total revenues on an annual basis.
American DG Energy has been considered a major customer in certain years, as disclosed in the accompanying financial statements;
however, we do not consider our business “dependent” upon its recurrence.

For the last two fiscal years, more than
half of our revenue was generated from long-term maintenance contracts, or service contracts, which provide us with a somewhat
predictable revenue stream, especially during the summer months. We have a slight surge of activity from May through September
as our “chiller season” is in full swing. Our service revenue has grown from year to year since 2005, with our New
York City/New Jersey, New England and to some extent California territories experiencing the majority of the growth. This growth
is consistent with the sale of new units into those territories. Our service margins are generally predictable as we service hundreds
of long-term contracts with relatively low dollar, high volume sales. Fluctuations at the job level are to be expected however,
due to the number of jobs, gross margin generally evens out in the aggregate.

26

Our product revenue is derived from the
sale of the various cogeneration modules, such as the InVerde 100, the CM-75 and the CM-60, and the three chiller models, such
as the smaller ST, the larger DT and the RT (roof-top) units. The sales cycle for each module varies widely, and can range from
as short as a month to as long as a year or more. The length of the sales cycle is generally dependent on the size of the project
and the number of decision makers in a customer’s facility. Furthermore, since our products and their installation are costly
they are considered a major capital improvement and customers may be slow in making their buying decisions. Our products sales
are high dollar value, low volume transactions. Therefore our product revenue can be difficult to predict and the expected margin
varies.

Our cogeneration and chiller modules are
built to order and revenue is recognized upon shipment. The lead time to build and deliver a unit depends on its customized configuration
and is approximately 12 to 16 weeks from time of purchase order. As revenue is recognized upon shipment, our work-in-process is
an important factor in understanding our financial condition in any given quarter.

Section 107 of the JOBS Act provides that
an emerging growth company can take advantage of the extended transition period provided in Section 7(a)(2)(B) of the Securities
Act for complying with new or revised accounting standards. However, we chose to “opt out” of any extended transition
period, and as a result we will comply with new or revised accounting standards on the relevant dates on which adoption of such
standards is required for non-emerging growth companies. Section 107 of the JOBS Act provides that our decision to opt out of the
extended transition period for complying with new or revised accounting standards is irrevocable.

Results of Operations

Year Ended December 31, 2013 Compared to Year Ended
December 31, 2012

Revenues

Revenues in 2013 were $15,849,869 compared
to $15,253,972 in 2012, an increase of $595,897 or 3.9%. This increase is largely due to an increase in service revenue during
the year as a result of increased installation revenue. Product revenues in 2013 were $6,346,050 compared to $7,453,222 in 2012,
a decrease of $1,107,172 or 14.9%. This decrease from the year ended December 31, 2012 to 2013 resulted from a decrease in
cogeneration sales of $591,763 and a decrease in chiller sales of $515,409. Our product mix, as well as product revenue, can vary
significantly from period to period as our products are high dollar, low volume sales in which revenue is only recognized upon
shipment. As a result, such fluctuation is expected.

Revenues derived from our service centers
including installation activities, in 2013 were $9,503,819 compared to $7,800,750 for the same period in 2012, an increase of $1,703,069
or 21.8%. Our service operation grows along with sales of cogeneration and chiller systems since the majority of our product sales
are accompanied by a service contract or time and materials agreements. As a result our “fleet” of units being serviced
by our service department grows with product sales. In addition, our service department revenue has increased due to turnkey projects
of $2,432,431 in 2013 compared to $711,259 in 2012.

27

Cost of Sales

Cost of sales in 2013 was $10,819,741 compared
to $9,388,898 in 2012, an increase of $1,430,843 or 15.2%. Our gross profit margin was 31.7% in 2013 compared to 38.4% in 2012,
a decrease of 6.7%. The decrease in gross profit margin is attributable to the margin on turnkey projects, that, although they
provide us with unit sales and the subsequent service contracts, the projects themselves provide a lower gross profit than our
traditional service business. In addition, this decrease is attributable to sales of certain Ilios units at below cost. These units
are among the first sold, and were sold at a loss in order to provide demonstration units for our sales representatives.

Contract Research and Development

Contract research and development income,
which is classified as an offset to applicable expenses, for the years ended December 31, 2013 and 2012 was $127,500 and $126,500,
respectively, a decrease of $1,000. The majority of this decrease is due to the completion of a research and development contract
which ended on June 30, 2011.

Operating Expenses

Operating expenses increased in 2013 to
$8,700,232 compared to $7,868,700 in 2012, an increase of $831,532 or 10.6%. This increase was due to increased investments in
research and development of approximately $436,000 compared to those of 2012, costs of $258,512 associated with an aborted public
offering in the third quarter of 2013, an increase in our selling efforts including attendance at trade shows and the related travel
expenses of approximately $150,000 and salaries, and various other expenses.

Selling expenses increased in 2013 to $1,423,587
compared to $1,225,580 for the same period in 2012 due to increased headcount in our sales and marketing departments. In addition,
during the year ended December 31, 2013 the Company invested approximately $200,000 in trade shows and a traveling “road
show” where three of the Company's products were showcased on an enclosed trailer which traveled through our key territories
on the east coast.

Loss from Operations

Loss from operations for the year ended
December 31, 2013 was $3,670,104 compared to $2,003,626 for the same period in 2012. The increase in the loss of $1,666,478
was due to the increase in operating expenses and reduction in gross profit as discussed above.

Other Income (Expense), net

Other expense, net for the year ended December 31,
2013 was $137,107 compared to $22,811 for the same period in 2012. Other income (expense) includes interest income and other income
of $3,958, net of interest expense on notes payable of $141,065 in 2013. For the same period in 2012, interest and other income
was $48,397 and interest expense was $71,208. The decrease in interest income of $44,439 is the result of a decrease in short-term
investments. The increase in interest expense of $69,857 was mainly due to demand notes and line of credit with an outstanding
balance of $1,200,000.

Provision for Income Taxes

We did not record any benefit or provision
for income taxes for the years ended December 31, 2013 and 2012, respectively. As of December 31, 2013 and 2012, the
income tax benefits generated from our net losses have been fully reserved.

28

Noncontrolling Interest

The noncontrolling interest share in the
losses of Ilios was $357,722 for the year ended December 31, 2013 compared to $389,480 for the same period in 2012, a decrease
of $31,758 or 8.2%. The decrease was due to a reduction in payroll costs that Ilios incurred in 2013, associated with the departure
of its Chief Operating Officer in May of 2013 and related forfeiture of stock compensation. Noncontrolling interest ownership percentage
as of December 31, 2013 and 2012 was 35.0%.

Net loss

Net loss for the year ended December 31,
2013 was $3,449,489 compared to $1,636,957 for the same period in 2012. The increase in the loss of $1,812,532 was due to the increase
in operating expenses and reduction in gross profit as discussed above.

Liquidity and Capital Resources

Consolidated working capital at December 31,
2013 was $5,565,789, compared to $4,078,704 at December 31, 2012, an increase of $1,487,085 or 36.5%. Included in working
capital were cash and cash equivalents of $7,713,899 at December 31, 2013, compared to $1,572,785 in cash and cash equivalents
and $181,859 in short-term investments at December 31, 2012.

Cash used in operating activities for the
years ended December 31, 2013 and 2012 was $3,384,019 and $3,152,782, respectively. Our accounts receivable balance increased
to $3,740,885 at December 31, 2013 compared to $2,700,243 at December 31, 2012, an increase of $1,091,242 due to timing
of billing, shipments and collections. Unbilled revenues also increased by $646,398 in connection with turnkey projects. Our inventory
decreased to $3,343,793 as of December 31, 2013 compared to $3,356,622 as of December 31, 2012, a decrease of $62,229.
Prepaid assets as of December 31, 2013 decreased to $340,013 compared to $402,846, a decrease of $62,833.

Accounts payable increased to $2,338,046
as of December 31, 2013 from $1,151,010 at December 31, 2012, an increase of $1,187,036. Accrued expenses increased to
$1,139,554 as of December 31, 2013 compared to $807,922 as of December 31, 2012, an increase of $331,632. Interest payable,
related party increased from $126,170 as of December 31, 2012 to $198,450 as of December 31, 2013, an increase of $83,560.

Our related party balance was a net receivable
of $55,837 as of December 31, 2012 and a net payable of $119,667 as of December 31, 2013. This change of $175,504 is
due to the remaining balance on the prepayment for future purchases, received from American DG Energy of $827,747 as on March 14,
2013.

During 2013 our cash flows from investing
activities were $916,389 and included sales of short-term investments of $182,061, purchases of property and equipment of $202,700,
expenditures related to intangible assets such as patents and product certifications of $397,950 and an acquisition of a product
line from a key vendor of $497,800.

Our cash flows from financing activities
were $10,441,522 for 2013, resulting from the proceeds of $5,966,805 from the sale of the Company's common stock in a private placement,
and the issuance of convertible debt of $3,000,000 and the issuance of demand notes payable of $1,650,000.

At December 31, 2013, our commitments
included various leases for office and warehouse facilities of $5,333,143 to be paid over several years through 2024. The source
of funds to fulfill these commitments will be provided either from cash and short-term investment balances, operations or through
debt or equity financing.

29

Based on our current operating plan, we
believe existing resources, including cash and cash flows from operations, will be sufficient to meet our working capital requirements
for the next twelve months. As we continue to grow our business, we expect that our cash requirements will increase. As a result,
we may need to raise additional capital through a debt financing or an equity offering to meet our operating and capital needs
for future growth.

Seasonality

We expect that the majority of our heating
systems sales will be in the winter and the majority of our chilling systems sales will be in the summer. Our cogeneration and
chiller system sales are not generally affected by the seasons, although customer goals will be to have chillers installed and
running in the spring. Our service team does experience higher demand in the warmer months when cooling is required. These units
are generally shut down in the winter and started up again in the spring. This “busy season” for the service team generally
runs from May through the end of September.

Off Balance Sheet Arrangements

On July 22, 2013, the Company’s Chief
Executive Officer personally pledged to support a bank credit facility of $1,055,000 to support bank guarantees issued on certain
construction contracts. This credit facility expires on July 22, 2014.

30

BUSINESS

Overview

Tecogen designs, manufactures, sells, and
services systems that produce electricity, hot water, and air conditioning for commercial installations and buildings and industrial
processes. These systems, powered by natural gas engines, are efficient because they drive electric generators or compressors,
which reduce the amount of electricity purchased from the utility, plus they use the engine’s waste heat for water heating,
space heating, and/or air conditioning at the customer’s building. We call this cogeneration technology CHP for combined
heat and power.

Tecogen manufactures three types of CHP
products:

•

Cogeneration units that supply electricity and hot water;

•

Chillers that provide air-conditioning and hot water; and

•

High-efficiency water heaters.

All of these are standardized, modular,
small-scale CHP products that reduce energy costs, carbon emissions, and dependence on the electric grid. Market drivers include
the price of natural gas, local electricity costs, and governmental energy policies, as well as customers’ desire to become
more socially responsible. Traditional customers for our cogeneration and chiller systems include hospitals and nursing homes,
colleges and universities, health clubs and spas, hotels and motels, office and retail buildings, food and beverage processors,
multi-unit residential buildings, laundries, ice rinks, swimming pools, factories, municipal buildings, and military installations;
however, the economic feasibility of using our systems is not limited to these customer types. Through our factory-owned service
centers in California, New York, Massachusetts, Connecticut, New Jersey, and Michigan our specialized technical staff maintain
our products through long-term contracts. We have shipped approximately 2,000 units, some of which have been operating for almost
25 years. We have 69 full-time employees and three part-time employees, including six sales and marketing personnel and 40 service
personnel.

Our CHP technology uses low-cost, mass-produced
engines manufactured by GM and Ford, which we modify to run on natural gas. In the case of our mainstay cogeneration and chiller
products, the engines have proved to be cost-effective and reliable. In 2009, our research team developed a low-cost process for
removing air pollutants from the engine exhaust. Because these systems are fueled by natural gas, they typically produce lower
levels of “criteria” air pollutants (those that are regulated by the EPA, because they can harm human health and the
environment) compared with systems fueled by propane, gasoline, distillates, or residual fuel oil. We offer our new Ultra
low-emissions technology as an option in our CHP systems.

After a successful field test of more than
a year, in 2012 we introduced the technology commercially as an option for all of our products under the trade name Ultra,
which was recently patented in the US in October 2013. The Ultra low-emissions technology repositions our engine-driven
products in the marketplace, making them comparable environmentally with emerging technologies such as fuel cells, but at a much
lower cost and greater efficiency.

Our products are designed as compact modular
units that are intended to be applied in multiples when utilized for larger CHP plants. Approximately 68% of our CHP modules are
installed in multi-unit sites ranging up to 12 units. This approach has significant advantages over utilizing single, larger units,
such as building placement in constrained urban settings and redundancy during service outages. Redundancy is particularly relevant
in regions where the electric utility has formulated tariff structures that have high “peak demand” charges. Such tariffs
are common in many areas of the country, and are applied by such utilities as Southern California Edison, Pacific Gas and Electric,
Consolidated Edison of New York, and National Grid of Massachusetts. Because these tariffs assess customers’ peak monthly
demand charge over a very short interval (typically only 15 minutes), a brief service outage for a system comprised of a single
unit is highly detrimental to the monthly savings of the system. For multiple unit sites, a full system outage is less likely and
consequently these customers have a greater probability of capturing peak demand savings.

31

Our in-licensed microgrid technology enables
our InVerde CHP products to provide backup power in the event of power outages that may be experienced by local, regional,
or national grids.

Our CHP products are sold directly to customers
by our in-house marketing team and by established sales agents and representatives, including American DG Energy and EuroSite Power
which are affiliated companies. We have shipped approximately 2,000 units, some of which have been operating for almost 25 years.
Our principal engine supplier is GM, and our principal generator supplier is Marathon Electric. To produce air conditioning, our
engines drive a compressor purchased from J&E Hall International.

In 2009, we created a subsidiary, Ilios,
to develop and distribute a line of high-efficiency heating products, starting with a water heater. We believe that these products
are much more efficient than conventional boilers in commercial buildings and industrial processes (see “Our Products”
below). As of the date of this prospectus, we own a 65.0% interest in Ilios.

Tecogen was formed in the early 1960s as
the Research and Development New Business Center of Thermo Electron Corporation, which is now Thermo Fisher Scientific Inc. For
the next 20 years, this group performed fundamental and applied research in many energy-related fields to develop new technologies.
During the late 1970s, new federal legislation enabled electricity customers to sell power back to their utility. Thermo Electron
saw a fit between the technology and know-how it possessed and the market for cogeneration systems.

In 1982, the Research and Development group
released its first major product, a 60-kilowatt, or kW, cogenerator. In the late 1980s and early 1990s, they introduced air-conditioning
and refrigeration products using the same gas engine-driven technology, beginning with a 150-ton chiller (tons are a measure of
air-conditioning capacity). In 1987, Tecogen was spun out as a separate entity by Thermo Electron and, in 1992, Tecogen became
a division of the newly formed Thermo Power Corporation.

In 2000, Thermo Power Corporation was dissolved,
and Tecogen was sold to private investors including Thermo Electron’s original founders, Dr. George N. Hatsopoulos and John
N. Hatsopoulos. Tecogen Inc. was incorporated in the State of Delaware on September 15, 2000. Our business and registered office
is located at 45 First Avenue, Waltham, Massachusetts, 02451. Our telephone number is 781-466-6400.

Industry Background

During the 20th
century, fossil-fuel power plants worldwide evolved toward large, complex central stations using high-temperature steam turbines.
This technology, though steadily refined, reached a maximum efficiency of about 40% that persists to this day. As used throughout,
efficiency means electrical energy output per unit of fuel energy input. According to the EPA website, the average efficiency of
fossil-fuel power plants in the United States is 33% and has remained virtually unchanged for four decades.

According to a 2002 report from the Northwest
Power Planning Council, titled “Natural Gas Combined-cycle Gas Turbine Power Plants,” the best efficiency obtainable
at the time of the report was about 50% from a combined-cycle steam turbine. More recent reports have expressed that comparable
efficiency rates are obtainable from a fuel cell. A combined-cycle system incorporates a second turbine powered by exhaust gases
from the first turbine. Large-scale replacement of existing power plants with combined-cycle technology would require considerable
capital investment and time. Fuel cells have high capital costs as well.

CHP, which harnesses waste energy from
the power generation process and puts it to work on-site, can boost the efficiency of energy conversion to nearly 90%, a better
than two-fold improvement over the average efficiency fossil fuel plant.

The implications of the CHP approach are
significant. If CHP were applied on a large scale, global fuel usage might be curtailed dramatically. Small on-site power systems,
in sizes like boilers and furnaces, would serve customers ranging from homeowners to large industrial plants. This is described
as “distributed” energy, in contrast to central power.

32

CHP became recognized in the late 1970s
as a technology important to aiding the reduction of fossil fuel consumption, pollution, and grid congestion. Since then, CHP
has been applied increasingly around the world. According to a report by the International Energy Agency, or IEA, titled “Cogeneration
and District Energy: Sustainable energy technologies for today...and tomorrow (2009), ” the value of CHP technology
to customers and policy makers stems from the fact that CHP systems are “inherently energy efficient and produce energy
where it is needed.”

According to the IEA report, the benefits
of CHP include:

•

Dramatically increased fuel efficiency;

•

Reduced emissions of carbon dioxide (CO2 ) and other pollutants;

•

Cost savings for the energy consumer;

•

Reduced need for transmission and distribution networks; and

•

Beneficial use of local energy resources, providing a transition to a low-carbon future.

CHP generates about 10% of the world’s
electricity. According to the IEA report, CHP could supply up to 24% of the energy generation of the Group of Eight + Five countries,
while meeting 40% of Europe’s target reductions in carbon emissions.

In the United States, CHP represents only
about 8% of the generating capacity. A paper issued by the United States Department of Energy, or DOE, in 2012, Combined Heat and
Power, A Clean Energy Solution, states that CHP is an underutilized resource. On August 30, 2012, the White House issued an executive
order, or the Executive Order, aimed at promoting investments in industrial energy efficiency, including CHP, and established a
national goal of deploying 40 GW (or 40,000 megawatts, or MW) of new CHP in the United States by 2020.

On-site CHP not only eliminates the loss
of electric power during transmission, but also offsets the capital expense of upgrading or expanding the utility infrastructure.
The national electric grid is already challenged to keep up with existing power demand. The grid consists of power generation plants
as well as the transmission and distribution network consisting of substations and wires.

Power plants are aging, and plans for new
power plants are on the decline (Figure 1). According to the U.S. Energy Information Administration’s “ Form EIA-860
Annual Electric Generator Report (2010),” the average age of a U.S. coal-fired power plant is 44 years. Coal plants account
for about 40% of the nation’s generation capacity.

In addition, the transmission and distribution
network is operating at capacity in urban areas. Decentralizing power generation by installing equipment at customer sites not
only relieves the capacity burden on existing power plants, but also unburdens transmission and distribution lines. This ultimately
improves the grid’s reliability and reduces the need for costly upgrades. Consolidated Edison, Inc., the electric utility
of New York City and surrounding areas, has identified an opportunity to integrate energy efficiency, distributed generation, and
demand response as a way to defer new infrastructure investments, according to the utility’s 2010 long-range plan.

We believe that increasingly favorable
economic conditions could improve our business prospects domestically and abroad. Specifically, we believe that natural gas prices
might increase from their current depressed values, but only modestly, while electric rates could go up over the long-term as utilities
pay for better emission controls, efficiency improvements, and the integration of renewable power sources. The net result of relative
gas and electric prices could be greater cost savings and annual rates of return to CHP customers.

Moreover, we believe that natural gas could
win favor politically as a domestic fuel with low carbon emissions. Government policy, both here and abroad, might promote CHP
as a way to conserve natural resources and reduce carbon and toxic emissions. Renewable wind and solar sources could encounter
practical limitations, while nuclear power is likely to be affected by its safety setbacks.

34

Tecogen’s Strategy for Growth

Target markets and new customers

The traditional markets for CHP systems
are buildings with long hours of operation and with coincident demand for electricity and heat. Traditional customers for our cogeneration
systems include hospitals and nursing homes, colleges and universities, health clubs and spas, hotels and motels, office and retail
buildings, food and beverage processors, multi-unit residential buildings, laundries, ice rinks, swimming pools, factories, municipal
buildings, and military installations.

Traditional customers for our chillers
overlap with those for our cogeneration systems. Chiller applications include schools, hospitals and nursing homes, office and
apartment buildings, hotels, retailers, ice rinks and industrial facilities. Engine-driven chillers are utilized as replacements
for aging electric chillers, since they both take up about the same amount of floor space.

The Company believes that the largest number
of potential new customers in the U.S. require less than 1,000 kW of electric power and less than 1,200 tons of cooling capacity.
We are targeting customers in states with high electricity rates in the commercial sector, such as California, Connecticut, Massachusetts,
New Hampshire, New Jersey, and New York. These regions also have high peak demand rates, which favor utilization of our modular
units in groups so as to assure redundancy and peak demand savings, as discussed above. Some of these regions also have generous
rebates that improve the economic viability of our systems.

As stated earlier, the U.S. government’s
goal, according to the Executive Order, is to deploy 40 GW (40,000 MW) of new CHP in the United States by 2020. In order to estimate
the share of that new deployment of CHP that is addressable by products in our size range, we reference a study done by ICF International
on the California market that breaks down projected market penetration by kW output range. According to the April 2010 Combined
Heat and Power Market Assessment, prepared for the California Energy Commission, in 2029, new CHP in the size range of our products
(50 kW to 500 kW), is projected to be 476 MW in the base case, or 684 MW if incentives such as carbon credits and power export
credits are considered. This size range constitutes 17.4% of the total California market potential in the base case, or 11% in
the case with incentives. If we assume California’s apportionment of small size CHP is applicable to the country, and conservatively
extend the government’s goal of 40,000 MW to 2029, we can estimate the U.S. market addressable by our products as 17.4% of
40,000 MW in the base case (11% with incentives) which amounts to 6,972 MW (4,416 MW with incentives). If we assume we can capture
30% of the market for CHP products in the size range of 50 kW to 500 kW, we can estimate that our potential for new unit sales
over the next twenty years is between 13,250 and 20,920 InVerde (100 kW) units, or approximately $1.5 to $2.4 billion in
revenue, at $112,500 per unit.

The largest market sectors identified by
ICF that are suitable for our products closely match our sales data from January 2007 through June 2012 (Figure 2).

The ICF report reveals CHP’s relatively
low existing market penetration in the smaller system sizes. Given that multi-megawatt CHP is already well-established (Table 1),
the market opportunity increases as size decreases. Small systems (less than one MW) may grow almost six-fold. The missed opportunity
is evident and likely even more disproportionate nationally. Most areas of the country, except the Northeast, are essentially without
significant market penetration of small-scale (less than 500 kW) CHP systems.

The DOE/EPA report confirms that CHP is
a “largely untapped resource” and states that there is significant technical market potential for CHP at commercial
and institutional facilities at just over 65 GW. This report also indicates that there was a significant decline in CHP in the
early 2000s due to deregulation of the power markets that resulted in market uncertainty and delayed energy investments. However,
a significant rebound and expansion of the CHP market may occur because of the following emerging drivers:

•

Changing outlook for natural gas supply and pricing as a result of shale exploration;

•

Growing state policymaking and support; and

•

Changing market conditions for the power and industrial sectors such as ageing power plants and boilers, as well as more strict
air regulations.

We intend to seek both domestic and international
customers in areas where utility pricing and government policy align with our advantages. These areas would include regions that
have strict emissions regulations, such as California, or those that reward CHP systems that are especially non-polluting, such
as New Jersey. There are currently 23 states that recognize CHP as part of their Renewable Portfolio Standards or Energy Efficiency
Resource Standards and several of them, including New York, California, Massachusetts, New Jersey, and North Carolina, have initiated
specific incentive programs for CHP (DOE/EPA report).

Our new microgrid capability, where multiple
InVerde units can be seamlessly isolated from the main utility grid in the event of an outage and re-connected to it afterward,
will likewise be exploited wherever utilities have resisted conventional generator interconnection but have conceded to UL-certified
inverters (such as Consolidated Edison in New York and Pacific Gas and Electric Company in California). Because our InVerde
systems operate independently from the grid, we also plan to exploit the need for outage security in certain market segments. These
segments include military bases, hospitals, nursing homes, and hotels.

As noted above in “Industry Background,”
the IEA report estimates that power from CHP produced by the Group of Eight + Five countries, currently at 10%, could increase
to 24% under a best-case scenario. We hope to participate in a robust international market, which we believe will be as large as
or larger than the domestic market.

Alliances

We continue to forge alliances with utilities,
government agencies, universities, research facilities, and manufacturers. We have already succeeded in developing new technologies
and products with several entities, including:

•

General Motors Company — supplier of raw materials pursuant to a supplier agreement since the development of
our cogeneration product in the early 1960s.

•

Sacramento Municipal Utility District — has provided test sites for the Company since 2010.

•

Southern California Gas Company and San Diego Gas & Electric Company, each a Sempra Energy subsidiary — have
granted us research and development contracts since 2004.

•

Lawrence Berkeley National Laboratory — research and development contracts since 2005.

•

Consortium for Electric Reliability Technology Solutions — research and development contracts and provided
a test site to the Company since 2005.

•

California Energy Commission — research and development contracts from 2004 until March 2013.

•

The AVL California Technology Center — support role in performance of research and development contracts as
well as internal research and development on our emission control system from August 2009 to November 2011.

37

We also have an exclusive licensing agreement
from the Wisconsin Alumni Research Foundation (WARF) for its proprietary control software that enables our microgrid system. The
software allows our products to be integrated as a microgrid, where multiple InVerde units can be seamlessly isolated from
the main utility grid in the event of an outage and re-connected to it afterward. The licensed software allows us to implement
such a microgrid with minimal control devices and associated complexity and cost. Tecogen pays WARF a royalty for each cogeneration
module sold using the licensed technology. Such royalty payments have been in the range of $5,000 to $20,000 on an annual basis
through the year ended December 31, 2013. In addition, WARF reserved the right to grant non-profit research institutions and
governmental agencies non-exclusive licenses to practice and use, for non-commercial research purposes technology developed by
Tecogen that is based on the licensed software.

Our efforts to forge partnerships continue
to focus on utilities, particularly to promote the InVerde, our most utility-friendly product. The nature of these alliances
varies by utility, but could include simplified interconnection, joint marketing, ownership options, peak demand mitigation agreements,
and customer services. We have commissioned a microgrid with the Sacramento Municipal Utility District at its headquarters in Sacramento,
California, where the central plant incorporated three InVerde systems equipped with our Ultra low-emissions technology.
Some expenses for this project were reimbursed to the utility through a grant from the California Energy Commission.

Certain components of our InVerde
product were developed through a grant from the California Energy Commission. This grant includes a requirement that we pay royalties
on all sales of all products related to the grant. As of December 31, 2012, such royalties accrued in accordance with this grant
agreement were less than $10,000 on an annual basis.

We also continue to leverage our resources
with government and industry funding, which has yielded a number of successful developments. These include the Ultra low-emissions
technology, sponsored by the California Energy Commission and Southern California Gas Company, and new 35-kW engine technology
we developed with the California Energy Commission’s support.

Pursuant to the terms of the grants from
the California Energy Commission, the California Energy Commission has a royalty-free, perpetual, non-exclusive license to these
technologies, for government purposes.

For the years ended December 31, 2013
and 2012, we spent approximately $866,700 and $384,500, respectively, in research and development activities, of which $127,500
and $126,500 was reimbursed through a grant agreement, respectively.

Tecogen’s Solution

Our CHP products address the inherent efficiency
limitation of central power plants by siting generation close to the loads being served. This allows customers with energy-intensive
buildings or processes to reduce energy costs and operate with a lower carbon footprint. Furthermore, with technology we have introduced
within the last two years, such as our Ultra low-emissions technology our products can now contribute to better air quality
at the local level.

According to our estimates and public sources,
our cogeneration systems convert nearly 90% of the natural gas fuel to useful energy in the form of electricity and hot water or
space heat. This compares to about 40% for central power. Other on-site upgrades such as insulation or lighting can help cut energy
use as well, but they do not displace nearly as much low-efficiency electricity. Our engine-driven chillers, when the waste heat
is effectively used, offer similar efficiency benefits compared with running an electric chiller plus a furnace or boiler.

Cogeneration and chiller products can often
reduce the customer’s operating costs (for the portion of the facility loads to which they are applied) by approximately
30% to 50% based on Company estimates, which provides an excellent rate of return on the equipment’s capital cost in many
areas of the country with high electricity rates. Our chillers are especially suited to regions where utilities impose extra charges
during times of peak usage, commonly called “demand” charges. In these cases, the gas-fueled chiller reduces the use
of electricity during the summer, the most costly time of year.

38

Our water heater product, introduced by
Ilios, operates like an electric heat pump but uses a natural gas engine instead of an electric motor to power the system (see
“Our Products” for an explanation of the heat pump). The gas engine’s waste heat is recovered and used in the
process, unlike its electric counterpart, which runs on power that has already lost its waste heat. As of December 31, 2013
, we have shipped eight Ilios water heaters and have additional two in inventory to fulfill current orders.

The net effect is that our heat pump’s
efficiency far surpasses that of conventional boilers for water heating. Similarly, if used for space heating, the engine-powered
heat pump would be more efficient than an electric heat pump, again because heat is recovered and used. The product’s higher
efficiency translates directly to lower fuel consumption and, for heavy use customers, significantly lower operating costs.

Our products also address the global objective
of reducing greenhouse gas emissions. When burned to generate power, natural gas produces lower carbon emissions per unit of energy
than any fossil fuel (Table 2), according to the EPA combined heat and power emissions calculator.

Table 2 — Fossil Fuel
Carbon Emissions

Source: EPA Emissions
Calculator

Fuel

CO2 emissions,
lbs/million Btu

Natural Gas

116.7

Distillate Oil

160.9

Coal

206.7

Our products, in addition to using the
lowest amount of carbon fuel, further reduce CO2 emissions (greenhouse gases) because of CHP’s
higher efficiency. Figure 3 compares the CO2 output of our products to that of the national
electric grid and other generation technologies. Our products are far superior to the grid and even outperform the CHP technologies
of fuel cells and microturbines.

39

Figure 3 — Comparison
of Carbon Emissions (GHG) for Various Sources

Including Tecogen’s CHP and Chiller
Products

Source: Tecogen
Inc.

(1)

Average U.S. Powerplant CO2 emission rate of 1,293 (lb/MWh) from USEPA eGrid 2010.

(2)

Coal Combined Cycle emissions based upon 50% efficiency (assumed to be the same as Natural Gas) and coal CO2
emission rate from EPA website.

Fuel Cell and Microturbine emissions based upon data listed in the ICF International Combined Heat and Power Market Assessment,
April 2010.

Furthermore, one Tecogen 100-kW CHP unit
will reduce carbon emissions by 390 tons per year (based on 8,000 run-hours), which, according to the EPA website’s calculator,
is the equivalent of 64 cars on the road. A microturbine of the same size would reduce carbon emissions by only 245 tons per year,
the equivalent of 41 cars, which is less than two-thirds the emissions reduction of our CHP product. Our Ilios water heater also
reduces CO2 emissions in proportion to its fuel savings.

In addition to reducing greenhouse gases,
our products with Ultra low-emission controls can improve air quality by reducing such pollutants as NOx and CO. Figure
4 presents the annual output of emissions of the InVerde unit equipped with the Ultra technology and compares it
to alternative energy technologies producing the equivalent energy output on an annual basis (100 kW, 670,000 Btu/hr). Thus, for
example, in lieu of an InVerde, a building would obtain electricity from a power plant and heat energy from a boiler. As
Figure 4 shows, the Ultra CHP system’s emissions are significantly less than the combined emissions of the power plant
and boiler for the same energy output.

40

Figure 5 presents the criteria pollutant
levels of the Ultra system versus alternative CHP sources of microturbines, fuel cells, and conventional reciprocating engines.
Microturbines and fuel cells, newer CHP technologies typically considered low-emission alternatives to engines, produce more NOx
than an Ultra engine CHP unit. Moreover, when compared to a conventional engine’s “best available control technology”
(BACT) as defined by the EPA for natural gas engines, both NOx and CO are reduced by nearly tenfold. Consequently, the Ultra
low-emissions technology is potentially transformative to the engine’s reputation in the energy marketplace, allowing it
to now be characterized as a source of clean power.

We manufacture natural gas engine-driven
cogeneration systems and chillers, all of which are CHP products that deliver more than one form of energy. We have simplified
CHP technology for inexperienced customers. Our cogeneration products are all standard, modular units that come pre-packaged from
the factory. They include everything the customer needs to minimize the cost and complexity of installing the equipment at a site.
The package incorporates the engine, generator, heat-recovery equipment, system controls, electrical switchgear, emission controls,
and modem for remote monitoring and data logging.

All of our cogeneration systems and most
of our chillers use the same engine, the TecoDrive 7400 model supplied by GM and modified by us to use natural gas fuel. The small
25-ton chiller uses a similar GM engine, the 3000 model. We worked closely with GM and the gas industry (including the Gas Research
Institute) in the 1980s and 1990s to modify the engine and validate its durability. For the Ilios water heater, we introduced a
more modern Ford engine that is enhanced for industrial applications. As of December 31, 2013, we have shipped eight Ilios
water heaters and have an additional two in inventory to fulfill current orders.

42

Our commercial product line includes:

•

The InVerde® and TECOGEN® cogeneration units;

•

TECOCHILL® chillers;

•

Ilios high-efficiency water heaters; and

•

Ultra low-emissions technology.

InVerde Cogeneration Units

Our premier cogeneration product is the
InVerde, a 100-kW CHP system that not only provides electricity and hot water, but also satisfies the growing customer demand
for operation during a utility outage, commonly referred to as “black-start” capability. The InVerde incorporates
an inverter, which converts direct current, or DC, electricity to alternating current, or AC. With an inverter, the engine and
generator can run at variable speeds, which maximize efficiency at varying loads. The inverter then converts the generator’s
variable output to the constant-frequency power required by customers (50 or 60 Hertz), as shown in Figure 6.

This inverter technology was developed
originally for solar and wind power generation. The company believes that the InVerde is the first commercial engine-based
CHP system to use an inverter. Electric utilities accept inverter technology as “safe” by virtue of its certification
to the Underwriters Laboratory interconnection standard (1741) — a status that the InVerde has acquired.
This qualifies our product for a much simpler permitting process nationwide and is mandatory in some areas such as New York City
and California. The inverter also improves the CHP system’s efficiency at partial load, when less heat and power are needed
by the customer.

The InVerde`s black-start feature
addresses a crucial demand from commercial and institutional customers who are increasingly concerned about utility grid blackouts
and brownouts, natural disasters, security threats, and antiquated utility infrastructure. Multiple InVerde units can operate
collectively as a standalone microgrid, which is a group of interconnected loads served by one or more power sources. The InVerde
is equipped with software that allows a cluster of units to seamlessly share the microgrid load without complex controls.

The InVerde CHP system was developed
in 2007, and we began shipping it in 2008. Our largest InVerde installation utilizes 12 units, which supply 1.2 MW of on-site
power and about 8.5 million Btu/hr of heat (700,000 Btu/hr per unit).

43

Figure 6 — Diagram of
InVerde CHP System

Source: Tecogen
Inc.

TECOGEN Cogeneration Units

The TECOGEN cogeneration system is the
original model introduced in the 1980s, which is available in sizes of 60 kW and 75 kW, producing up to 500,000 Btu/hr of hot water.
This technology is based on a conventional single-speed generator. It is meant only for grid-connected operation and is not universally
accepted by utilities for interconnection, in contrast to the InVerde. Although this cogeneration product has the longest
legacy and largest population, much of its production volume has been supplanted by the InVerde.

TECOCHILL Chillers

Our TECOCHILL natural gas engine-driven
chillers are available in capacities ranging from 25 to 400 tons, with the smaller units air-cooled and the larger ones water-cooled.
This technology was developed in 1987. The engine drives a compressor that makes chilled water, while the engine’s free waste
heat can be recovered to satisfy the building’s needs for hot water or heat. This process is sometimes referred to as “mechanical”
cogeneration, as it generates no electrical power, and the equipment does not have to be connected to the utility grid.

A gas-fueled chiller provides enough air
conditioning to avoid most of the utility’s seasonal peak charges for electric usage and capacity. In summer when electric
rates are at their highest, natural gas is “off-peak” and quite affordable. Gas-fueled chillers also free up the building’s
existing electrical capacity to use for other loads.

Ilios High-Efficiency Water Heaters

Our newest product, the Ilios high-efficiency
water heater, uses a heat pump, which captures warmth from outdoor air even if it is moderately cool outside. Heat pumps work somewhat
like a refrigerator, but in reverse. Refrigerators extract heat from inside the refrigerator and move it outside the refrigerator.
Heat pumps extract heat from outside and move it indoors. In both cases, fluids move the heat around by flowing through heat exchangers.
At various points the fluids are compressed or expanded, which absorbs or releases heat.

44

In the Ilios water heater, the heat pump
moves heat from outdoors to the water being heated in the customer’s building. The heat pump water heater serves as a boiler,
producing hot water for drinking and washing or for space heating, swimming pools, or other building loads. Energy cost savings
to the customer depend on the climate. Heat pumps in general (whether gas or electric) perform best in moderate weather conditions.

In a conventional electric heat pump, the
compressor is driven by an electric motor. In the Ilios design, a natural gas-fueled engine drives the compressor. This means that
the heat being captured from outdoors is supplemented by the engine’s waste heat, which increases the efficiency of the process.
According to scientific studies, gas engine heat pumps can deliver efficiencies in excess of 200%.

UltraLow-Emissions Technology

All of our CHP products are available with
the Ultra low-emissions technology. This breakthrough technology was developed in 2009 and 2010 as part of a research effort
funded by the California Energy Commission and Southern California Gas Company. The objective was to bring our emission control
systems into compliance with California’s standards, which are the most stringent in the United States.

We were able to meet or exceed the standards
with an emission control system that is cost-effective, robust, and reliable. The Ultra low-emissions technology keeps our
CHP systems compliant with air quality regulations over the long term. Given the proprietary nature of this work, we obtained a
patent in the United States and have filed patents that are pending in Europe, Australia, Brazil, Canada, China, Costa Rica, the
Dominican Republic, India, Israel, Japan, Mexico, New Zealand, Nicaragua, Republic of Korea, Singapore, and South Africa. We shipped
the first commercial CHP units equipped with Ultra low-emissions technology to a California utility in 2011.

We conducted three validation programs
for this technology:

1.

Third-party laboratory verification. The AVL California Technology Center, a long-standing research and technology partner with the international automotive industry, confirmed our results in their state-of-the-art dynamometer test cell, which was outfitted with sophisticated emissions measurement equipment.

2.

Verifying longevity and reliability in the field. We did so by equipping one of our TECOGEN 75-kW units, already operating at a customer location in Southern California, with the Ultra low-emissions technology and a device to monitor emissions continuously. To date, the Ultra low-emissions system has operated successfully for more than 25,000 hours (more than three years) and has consistently complied with California’s emission standards. This field test is ongoing.

3.

Additional independent tests. During the field test, two companies licensed in California to test emissions each verified our results at different times. The results from one of these tests (obtained in August 2011) enabled us to qualify for New Jersey’s fast-track permitting. Virtually every state nationwide requires some kind of permit related to local air quality, but New Jersey allows an exemption for systems such as ours that demonstrate superior emissions performance. This certification was granted in November 2011, and since then we have sold Ultra low-emissions systems to several customers.

In 2012, a 75 kW CHP unit equipped with
the Ultra system became our first unit to obtain a conditional air permit (i.e. pending a third party source test to verify
compliance) in Southern California since the strict regulations went into place in 2009. A state-certified source test, administered
in January 2013, verified that our emissions levels were well below the new permitting requirements, and the final permit version
was approved in August 2013. To date, we have shipped over fifty units fitted with the Ultra system to sites in the Northeast,
as well as California.

45

Contributions to Revenue

The following table summarizes net revenue
by product line and services for the years ended December 31, 2013 and 2012:

December 31, 2013

December 31, 2012

Products:

Cogeneration

$

5,199,649

$

5,791,412

Chiller

1,146,401

1,661,810

Total Product Revenue

6,346,050

7,453,222

Services

7,071,388

7,089,491

Installations

2,432,431

711,259

Total Service Revenue

9,503,819

7,800,750

Total Revenue

$

15,849,869

$

15,253,972

All of the Company’s long lived assets
reside in the United States of America. All of the Company’s revenue is generated in the United States of America.

Segments

The Company’s operations are comprised
of one business segment. Our business is to manufacture and support highly efficient CHP products based on engines fueled by natural
gas.

Product Reliability

Our product lines have a long history of
reliable operation. Since 1995, we have had a remote monitoring system in place that connects to hundreds of units daily and reports
their “availability,” which is the amount of time a unit is running or is ready to run (% of hours). Figure 7 shows
cumulative data for an installed base of 340 units. More than 80% of them operate above 90% availability, with the average being
93.8%. By comparison, the average availability for all fossil-fueled power plants in the United States was 87.5% during 2006 –
2010, according to a report by the North American Electric Reliability Corporation.

46

Figure 7 — Tecogen Product
Reliability

Source: Tecogen
Inc. – January 2014

Product Service

We provide long-term maintenance contracts,
parts sales, and turnkey installation through a network of eight well-established field service centers in California, the Midwest,
and the Northeast. These centers are staffed by full-time Tecogen technicians, working from local leased facilities. The facilities
provide offices and warehouse space for inventory. We encourage our customers to provide Internet or phone connections to our units
so that we can maintain communications, in which case we contact the machines daily, download their status, and provide regular
operational reports (daily, monthly, and quarterly) to our service managers. This communication link is used to support the diagnosis
effort of our service staff and to send messages to preprogrammed phones that a unit has experienced an unscheduled shutdown.

Our service managers, supervisors, and
technicians work exclusively on our products. Because we manufacture our own equipment, our service technicians bring hands-on
experience and competence to their jobs. They are trained at our manufacturing facility in Waltham, Massachusetts.

Most of our service revenue is in the form
of annual service contracts, which are typically of an all-inclusive “bumper-to-bumper” type, with billing amounts
proportional to achieved operating hours for the period. Customers are thus invoiced in level, predictable amounts without unforeseen
add-ons for such items as unscheduled repairs or engine replacements. We strive to maintain these contracts for many years, so
that the integrity and performance of the machine are maintained. Between 2007 and 2012, approximately 68% of customers signed
service contracts.

R&D Capabilities

Our research and development tradition
and ongoing programs have allowed us to cultivate deep engineering expertise and maintain continuity over several decades. We have
strong core technical knowledge that is critical to product support and enhancements. Our TecoDrive engine, cogeneration and chiller
products, InVerde, and most recently the InVerde Ultra and Ilios heat pump water heater were all created and optimized
with both public and private funding support.

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In March 2013, we successfully completed
a $1 million program with the California Energy Commission, which was awarded in 2009, to develop a small CHP engine (about 35
kW) that uses advanced automotive technology. The engine achieves a nearly 20% fuel efficiency gain over our current TecoDrive
technology. The program included an endurance test to qualify the engine for the CHP duty cycle. Final development work to transition
to the 2012 model year advanced engine took place in 2013, with rollout on the Ilios water heating product anticipated in late
2014. In 2015, we plan to develop a smaller InVerde unit (~35 kW) around this engine platform.

In October 2012, Tecogen was awarded a
contract for a demonstration project to retrofit a natural-gas powered municipal water pump engine with Tecogen’s proprietary
Ultra low-emissions technology. This project, co-sponsored by Southern California Gas Co. (SoCalGas), DE Solutions, and
the Eastern Municipal Water District (EMWD) will be the first application of Tecogen’s emission control technology on a non-Tecogen
engine, and an important proof of concept for its wider application. This system was commissioned in September 2013.

Tecogen also continues to support a contract
with the DOE’s Lawrence Berkeley National Laboratory, awarded in 2012, for microgrid development work related to the InVerde.

Distribution Methods

Our products are sold directly to end-users
by our sales team and by established sales agents and representatives. Various agreements are in place with distributors and outside
sales representatives, who are compensated by commissions, including American DG Energy, which is an affiliated company, for certain
territories and product lines. For example, we have sales representatives for the chiller market in the New York City/New Jersey
territory, but we do not have a sales representative for our cogeneration products in this territory. In New England, our affiliate,
American DG Energy, has exclusive sales representation rights to our cogeneration products only (not including chillers). Sales
through our in-house team or sales that are not covered by a representative’s territory carry no commission or only a fractional
one.

Our CHP products are all standard, modular units that come pre-packaged from the factory to simplify installation and grid
connection. The systems are supported in the field by a nationwide network of experienced professional staff. Standardized CHP
units, as opposed to custom-designed systems, achieve lower cost, better quality control, higher reliability, and easier service.
Emission controls are integrated, and complete system warranty and maintenance are available.

•

Our Ultra low-emissions technology eliminates the air quality concerns associated with engines. Our units comply with
the most rigorous air quality regulations, including California’s.

•

Our cogeneration systems and chillers use standard, well-proven equipment made by reputable, well-established manufacturers.
These components include rugged automotive engines, certified inverters, commercial generators, and conventional compressors. Certain
key components are proprietary and have patent protection. Most notably, all control software is either proprietary (and copyright
protected) or under an exclusive license agreement. Suppliers of the InVerde `s inverter and generator hold certain related
patent protection.

•

All of our CHP products can be designed for installation of multiple units at a single site, depending on the customer’s
particular needs. This enhances the ability of our products to meet the building’s varying demand for electricity, heat,
and/or air conditioning throughout the day and from season to season. Also, multiple units operate more efficiently throughout
the range of a customer’s high and low energy requirements.

The InVerde overcomes barriers related to grid interconnection, since the product is UL-certified as utility-safe. In
microgrids, InVerde units can help prevent brownouts by maximizing their power output when utilities approach peak capacity.
Unlike standby diesel generators, the InVerde can operate without hourly limits because its emissions are so low, and it
can serve as a stable anchor in hybrid microgrids that incorporate solar power.

•

Our extensive use of standardized components lets us manufacture CHP products at competitive prices, even at relatively low
production volumes. Proven, well-understood hardware increases the reliability and durability of the equipment and reduces the
cost of servicing in the field. We are also able to minimize spare parts inventories and simplify training requirements.

•

The Ilios heat pump water heater roughly doubles the efficiency of conventional water heating systems. The Ilios heat pump
targets a large international market that is characterized by heavy, year-round use. This will increase fuel savings and maximize
return on investment for the customer. Also, such applications are mostly central heating and cooling systems, rather than units
distributed throughout the building, so it is easier to integrate new equipment. The heat pump water heater product competes only
against other gas-fueled water heaters, which could expand our market beyond areas with high electric rates, and regulatory issues
should be minimal.

Competitive Position and Business Conditions

Our products fall into the broad market
category of distributed generation systems that produce electric power on-site to mitigate the drawbacks of traditional central
power and the low efficiency of conventional heating processes.

Renewable power sources, such as wind and
solar, do not improve heating inefficiencies as CHP systems do, so they do not compete with our products. That is, CHP utilization
is based on the redirection of fuel from an onsite boiler to an engine (or other device) for the production of electricity; the
waste heat from the engine meets the heating load of the site with only a small incremental fuel consumption increase, but with
the benefit of a significant amount of electricity production. As the boiler output cannot be displaced by renewable electricity
production — the output of which is far more valuable displacing utility electric power, than used for water heating — the
CHP opportunity remains available even in sites fully exploited relative to their renewable potential.

Cogeneration Systems

The ICF report breaks down the CHP market
by technology as provided in Figure 8 below. We believe the California data applies to the domestic and international CHP market
as a whole.

Our CHP products use automotive reciprocating
engines originally designed for gasoline fuel and modified to run on natural gas. Diesel-fueled reciprocating engines will remain
prominent in the CHP market, but only in larger, custom-designed systems (one MW or more), so these products do not compete with
ours.

In smaller CHP sizes, competitors have
duplicated our older design, coupling an automotive engine to a single-speed generator and adding controls and heat recovery. To
be competitive with our designs, however, they would have to acquire comparable experience in the equipment and technology, installation
contracting, maintenance and operation, economic evaluation of candidate sites, project financing, and energy sales, as well as
the ability to cover broad regions. They would also have to meet the price of our products, which is low because we use standardized
components.

We believe that no other company has developed
a product that competes with our inverter-based InVerde, which offers UL-certified grid connection, outage capability, and
variable-speed operation. We anticipate that an inverter-based product with at least some of these features will be introduced
by others, but we believe that they will face serious challenges in duplicating the InVerde. Product development time and
costs would be significant, and we expect that our patents and license for microgrid software will keep others from offering certain
important functions.

Our patent application relating to the
Ultra low-emissions technology was issued by the U.S. PTO in October 2013. We expect that this will make the development
of alternative technologies by competitors difficult. If this is the case, we could retain a strong competitive advantage for all
our products in markets where severe emissions limits are imposed or where very clean power is favored, such as New Jersey, California,
and Massachusetts.

Newer technologies, such as fuel cells
and microturbines, pose limited competition to our CHP products. ICF International’s 2010 CHP market assessment provides
a comparison of the various small CHP technologies (50 – 500 kW), and a summary of this study is presented in Table 3. As
shown, reciprocating engine CHP enjoys an economic advantage, as it has just over one-third the installed cost of a fuel cell and
costs 20% less than a microturbine. With regard to operation and maintenance (O&M) costs, engine O&M costs are slightly
less than those of microturbines, and just over half those of fuel cells. Although fuel cells have the highest electric efficiency
(36%), they also have the lowest thermal output, so often fuel cells cannot recover enough heat to serve building loads effectively.
Microturbines also recover less heat than engine CHP and have a lower electric efficiency. As a result, typical reciprocating engine
CHP has the most favorable overall efficiency, at 79%, compared to 72% for microturbines and 67% for fuel cells.

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With regard to pollutant emissions, Figure
5, above, compares all three technologies, along with the Tecogen engine CHP equipped with the Ultra technology. This figure
illustrates that although fuel cells and microturbines are cleaner than conventional engine CHP (i.e., BACT), an engine equipped
with Ultra technology now has comparable emissions to these other two technologies.

In the growing microgrid segment, neither
fuel cells nor microturbines can respond to changing energy loads when the system is disconnected from the utility grid. Engines
inherently have a fast dynamic response to step load changes, which is why they are the primary choice for emergency generators.
Fuel cells and microturbines would require an additional energy storage device to be utilized in off-grid operation.

Most manufacturers of microturbines have
refocused on other markets. We believe that Capstone Turbine Corporation is the only microturbine manufacturer with a commercial
presence in CHP. Figure 9 reveals the modest impact of both microturbines and fuel cells in California’s CHP space.

According to the Energy Solutions Center
(a non-profit consortium), three companies make gas-engine-driven chillers that compete with our products: Trane, a division of
Ingersoll-Rand plc, York, a division of Johnson Controls, Inc. and Alturdyne. Natural gas can also fuel absorption chillers, which
use fluids to transfer heat without an engine drive.

Today’s low natural gas prices in
the United States improve the economics of gas-fueled chillers, so more competition could emerge. However, engine chillers will
continue to have an efficiency advantage over absorption machines. Chiller performance is measured in terms of cooling energy output
per unit of fuel input. This industry standard is called the coefficient of performance, or COP. Absorption chillers achieve COPs
of about 1.2 (see, for example, The Chartered Institution of Building Services Engineers’ Datasheet 07, Absorption Cooling,
February 2012). Our TECOCHILL products reach efficiencies well above that level (COPs ranging from 1.6 to 2.6).

Ilios Engine-Driven Heat Pump

Although a few companies manufacture gas-engine
heat pumps, their products are not directly comparable to the Ilios. The Ilios water heater and other heat pump products compete
in both the high-efficiency water heating market and the CHP market. In a typical building, the Ilios heat pump would be added
on to an existing heating/water heating system, but would be operated as many hours as possible. The conventional boiler would
be left in place, but would serve mainly as a backup when the heat pump’s engine is down for maintenance or when the heat
pump cannot meet the building’s peak heating load.

The best customers for the Ilios heat pump
water heater would be very similar to those for traditional CHP — heavy consumers of hot water and process heat.
In areas where low electric rates make CHP not economical, the Ilios heat pump could be a financially attractive alternative because
its economics depend only on natural gas rates. In some areas with high electric rates, the Ilios option could have advantages
over CHP. For example, where it is hard to connect to the utility grid or where the building’s need for electricity is too
low for CHP to work economically. As of December 31, 2013, we have shipped eight Ilios water heaters and have an additional
two in inventory to fulfill current orders.

Intellectual Property

We currently hold three United States patents
for our technologies:

•

8,578,704: “Assembly and method for reducing nitrogen oxides, carbon monoxide, and hydrocarbons in exhausts of internal
combustion engines.” This patent, granted in November 2013, is for the Ultra emission system applicable to all our
products.

•

7,239,034: “Engine driven power inverter system with cogeneration”. This patent, granted in July 2007, pertains
to the utilization of an engine-driven CHP module combined with an inverter and applies to our InVerde product specifically.

•

7,243,017: “Method for controlling internal combustion engine emissions”. This patent, granted in July 2007, applies
to the specific algorithms used in our engine controller for metering the fuel usage to obtain the correct combustion mixture.
It applies to most of our engines.

In addition, we have licensed specific
rights to microgrid algorithms developed by University of Wisconsin researchers for which we pay royalties to the assignee, The
Wisconsin Alumni Research Foundation (WARF). The specific patent named in our agreement is “Control of small distributed
energy resources” (7,116,010), granted in 2006. Our specific rights are valid for engine-driven systems utilizing natural
gas or diesel fuel in the application of power generation where the per unit output is less than 500 kW.

We consider our patents and license to
be important in the present operation of our business. The expiration, termination, or invalidity of one or more of these patents
may have a material adverse effect on our business. Our earliest patent, that licensed from WARF, was issued in 2006 and expires
in 2022. Most of our patents expire between 2022 and 2027.

52

We believe that no other company has developed
a product that competes with our inverter-based InVerde. We anticipate that an inverter-based product with at least some
of these features will be introduced by others, but we believe that competitors will face serious challenges in duplicating the
InVerde. Product development time and costs would likely be significant, and we expect that our patent for the inverter-based
CHP system (7,239,034) would offer significant protection, especially in key features. Likewise, we consider the microgrid license
with WARF to be a key feature of our InVerde product, and one that would be difficult to duplicate outside the patent.

The recent issuance by the U.S. PTO of
the patent for the Ultra low-emissions technology keeps that technology exclusive to us. It applies to all of our gas engine-driven
products and may have licensing applications to other natural gas engines. We have also filed for patents for this technology in
Europe, Australia, Brazil, Canada, China, Costa Rica, the Dominican Republic, India, Israel, Japan, Mexico, New Zealand, Nicaragua,
Republic of Korea, Singapore, and South Africa. There is no assurance, however, that the Ultra low-emissions patent applications
will be approved in any other country.

Government Regulation and Its Effect on
Our Business

Several kinds of government regulations
affect our current and future business, such as:

•

Product safety certifications and interconnection requirements;

•

Air pollution regulations, which govern the emissions allowed in engine exhaust;

•

State and federal incentives for CHP technology; and

•

Electric utility pricing and related regulations.

Regulations that control air quality and
greenhouse gases might increasingly favor our low-emission products. Regulations related to utility rates and interconnections,
which are burdensome today, could evolve to embrace CHP because of its efficiency benefits.

Product Safety Certifications and Interconnection
Requirements

Our products must comply with various local
building codes and must undergo inspection by local authorities. Our products are also certified by a third party to conform to
specific standards. These certifications require continuous verification by a company that monitors our processes and design every
three months. Our InVerde product is also certified to Europe’s standard CE mark (European Conformity), which is mandatory
for products imported into the European Union for commercial sale.

Our cogeneration CHP products are also
certified to a particular group of standards specific to the distributed power industry, which are used in the utility interconnection
permitting process. These unique certifications were developed by various manufacturers, utilities, and government regulators to
standardize the process of getting the utility’s permission to jointly power a facility.

In essence, manufacturers of standard products
are allowed to submit a sample unit to be “type-tested” by a Nationally Recognized Testing Laboratory. This test proves
that the product adheres to safety requirements and that its design is fail-safe. The product then becomes eligible for a fast-track
interconnection, after passing simple site-specific screens. Under state-mandated regulations, such as California Rule 21 and Massachusetts
Interconnection Tariff 09-03, most utilities must accept the fast-track process, which includes the certification.

53

Simplified utility interconnection is important
to CHP projects, so our interconnect certification, Underwriters Laboratory Standard 1741, or UL Certification, is a significant
competitive advantage. Obtaining the UL Certification was a major reason for us to develop the inverter-based CHP product. As with
our other product certifications, we plan to maintain the certification through routine processes when modest design changes occur.
When complete recertification is required, such as when a new revision to the standard is applicable or when the design undergoes
a major upgrade, the company will follow the normal procedures for first-time certification (third party design review and test
verification). The company does not anticipate any changes to the standard that would preclude recertification, as the underlying
content is carefully administered by balanced committees (representing utilities, inverter suppliers, and academia). In addition,
the standard and its utilization as the criterion for systems to qualify for simplified interconnection programs, is important
for the solar PV industry. The company believes that this importance to the solar industry will help assure the long-term relevance
in interconnection of distributed generation devices.

Air Pollution Regulations

Stationary natural gas engines are subject
to emissions regulations that are part of a complex hierarchy of state and federal regulations. The EPA establishes technology-specific
standards that are based on cost-benefit analysis for emission control strategies. These standards, termed BACT (best available
control technology), are imposed in regions that fail to meet federal clean air standards. Local regulators can and do restrict
engine emissions to lower levels.

In some instances, regional standards in
our key markets have become sufficiently strict, presenting a challenge in controlling pollution from natural gas engines. However,
our development of the Ultra low-emissions technology has addressed this issue, allowing us to permit our equipment in the
strictest region of Southern California. In January 2013, a state-certified source test at a new customer’s site verified
that our emissions levels were well below the new permitting requirements. Since we have now successfully removed this barrier,
we are not only competitive in the California market, but have an advantage as a cleaner CHP technology. Likewise, in the Northeast
where emissions regulations are trending towards California levels, we have already established our Ultra CHP as a certified
technology in New Jersey, exempt from the air permitting process and subsequent testing, a unique status that separates us from
the competition.

On the East Coast, important CHP territories
are also moving toward limits below federal BACT levels. Effective in 2012, Massachusetts, Rhode Island, and Connecticut require
3.6 ppm NOx and about 56 ppm CO, which is on par with California’s BACT standard. New Jersey also emulates California’s
BACT, but allows the project to side-step the air permit process if the CHP device is “emissions certified” through
third-party testing to 10 ppm NOx and 10 ppm CO. Our Ultra low-emissions technology has qualified for New Jersey’s
“clean” certification, as noted earlier. In New York, clean power is encouraged through state grants that exclude products,
or reduce the grant amount, unless low emissions are demonstrated.

Air emissions regulations also affect our
air conditioning and Ilios heat pump products, though the effects are muted. TECOCHILL rebates are not common, and none has been
tied to a specific emissions level. The heat pump’s small size often exempts it from regulations, and the market for heat
pump products could lie in lightly regulated regions (those with low electric rates). Nevertheless, the Ultra low-emissions
technology can be applied to these products if required to meet regulatory standards.

State and Federal Incentives

On August 30, 2012, the White House released
an Executive Order to accelerate investments in industrial energy efficiency, including CHP. The goal of the Executive Order is
to supply 40 GW of energy by 2020 from greater efficiency sources such as CHP systems. The DOE, Commerce, and Agriculture, and
the Environmental Protection Agency, or EPA, in coordination with the National Economic Council, the Domestic Policy Council, the
Council on Environmental Quality, and the Office of Science and Technology Policy, shall coordinate policies to encourage investment
in industrial efficiency in order to reduce costs for industrial users, improve U.S. competitiveness, create jobs, and reduce harmful
air pollution. With this Executive Order, it is expected that barriers to CHP development will be removed with effective programs,
policies, and financing opportunities, resulting in $40 – $80 billion in new capital investment in CHP. This initiative by
the U.S. government may boost CHP awareness and stimulate market activity.

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In addition, some states offer incentives
to CHP systems. New York and New Jersey have incentive programs that rebate a significant portion of the CHP project cost. Similar
incentive programs also exist in Massachusetts, Rhode Island, and Maryland albeit with different structures and terms. Massachusetts
has an additional CHP incentive in the form of an annual rebate proportional to the carbon savings versus conventional technology.

Also our products installed before 2010
are eligible for the bonus depreciation included in the 2009 American Recovery and Reinvestment Act, and our products installed
between January 1, 2008 and December 31, 2013 are eligible for the bonus depreciation included in the 2012 American Taxpayer Relief
Act. Also, the Energy Improvement and Extension Act of 2008 provides a 10% investment tax credit through 2016 for CHP in our size
range, which applies to the total project cost. Our TECOCHILL and heat pump products also qualify for the credit when heat recovery
achieves a minimum 60% efficiency.

Electric Utility Pricing and Related Regulations

Electricity prices, rate structures, and
tariffs are another form of government incentive or disincentive. Utility pricing is administered through state agencies, typically
public utility commissions, through formal proceedings involving the public, utilities, and various affected parties. Often, direct
legislative mandates apply to specific issues. How these rules are structured and interpreted has a significant impact on the economic
viability of CHP. These rules have hurt the CHP industry in the past, but we have designed our products to undermine their impact.

Demand Charges. Many
electric utilities structure their commercial rates such that part of the customer’s bill is fixed charges such as meter
fees, and part is peak demand charges, which are a much larger line-item based on the building’s maximum short-term usage
(typically 15 minutes). Fixed charges, usually small, are not addressed by CHP technology. Avoidance of peak demand charges requires
a CHP system to always operate at extremely high efficiency, which is difficult to achieve in practice.

Our CHP products, being small and modular,
are often installed as multiple units. This protects the customer to some degree from incurring peak demand charges at the full
system rating by providing equipment redundancy. The customer would then have to buy more electricity to make up for it, possibly
incurring a large demand charge. With a modular, multi-unit CHP system, all the units would have to fail simultaneously to incur
an equivalent charge.

Our TECOCHILLs are highly effective in
eliminating not only summertime electricity usage, but also peak demand charges. The chiller’s operation is confined to the
cooling season, allowing maintenance to be scheduled for other times. Outages during the cooling season can be managed to minimize
their impact.

Avoided-Cost Penalties. In
some regions, utilities have argued that CHP customers, by reducing their electric usage, have avoided paying their fair share
of the costs associated with grid infrastructure. To correct this perceived inequity, some utilities have successfully petitioned
their state commissions to impose a “departing load charge.” Utilities have also been allowed to add a “standby”
surcharge to compensate for the cost of utility power being available when the CHP system is down.

These types of charges are not prevalent
in East Coast states, but both standby and departing load charges are well-established in California. Although our CHP products
are affected, our chillers and heat pumps are not.

Technology-Specific Net Metering. Interconnection
issues are safety-related and should be product-neutral, but technology bias is common. In many states, CHP is excluded from net
metering while other technologies are eligible. Under net metering, utilities must pay on-site generators for excess electricity
that is fed into the grid. Net metering makes it easier to manage the operation of a CHP system or other generator.

55

Other Utility-Related Regulations. Another
category of utility regulation that might affect our business is Renewable Portfolio Standards, or RPS. As of December 2013, some
form of portfolio standards had been established in 38 states and the District of Columbia. According to the EPA, out of these
states, 26 — Arizona, Connecticut, Delaware, Colorado, Hawaii, Illinois, Indiana, Louisiana, Maine, Massachusetts,
Michigan, Minnesota, Nevada, New Hampshire, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, Rhode Island,
South Dakota, Utah, Vermont, Washington and West Virginia — specifically mention CHP and/or waste heat-to-power
as eligible under their RPS (or related efficiency/clean energy program guidelines). RPS-type mechanisms have been adopted in several
other countries, including Britain, Italy, Poland, Sweden, Belgium, and Chile.

Overall, RPS appears to be a positive policy
for Tecogen and CHP. Program structures, if fair and balanced, encourage less fossil fuel use by offering financial incentives
to improve efficiency. Electric power generated from renewable sources would tend to increase overall electric rates and improve
CHP investment returns. Since these programs are in their early stages, their impact is yet to be determined.

A national carbon “cap and trade”
program is not anticipated in the foreseeable future. Cap and trade programs seek to reduce carbon emissions by putting a price
on them. Of possible impact to Tecogen is the cap and trade bill moving forward in the California legislature. The program’s
details are still being reviewed and negotiated by various government and advocacy groups.

Employees

As of December 31, 2013, we employed
69 full-time employees and three part-time employees. We believe that our relationship with our employees is satisfactory. Three
of our New Jersey service employees are represented by a collective bargaining agreement which was executed on February 25,
2014 with a retroactive effective date of January 1, 2014. This agreement expires on December 31, 2016.

Properties

Our headquarters is located in Waltham,
Massachusetts, and consists of approximately 43,000 square feet of leased space, of which Tecogen occupies approximately 34,600
square feet of manufacturing, storage and office space. We sub-lease the remaining space to Ilios, American DG Energy, and other
tenants. Our lease, with an original expiration date of March 31, 2014, was renewed for an additional ten years and will expire
March 31, 2024. We believe that our facilities are appropriate and adequate for our current needs.

Legal Proceedings

From time to time, we may become party
to litigation or other legal proceedings that we consider to be a part of the ordinary course of our business. We are not currently
involved in legal proceedings that could reasonably be expected to have a material adverse effect on our business, prospects, financial
condition, or results of operations. We may become involved in material legal proceedings in the future.

56

MANAGEMENT AND GOVERNANCE

Directors and Executive Officers

The following table lists the current
members of our Board of Directors and our executive officers. The address for our directors and officers is c/o Tecogen Inc.,
45 First Avenue, Waltham, Massachusetts 02451.

Name

Age

Position(s)

Angelina M. Galiteva

47

Chairperson of the Board of Directors

John N. Hatsopoulos

80

Chief Executive Officer and Director

Robert A. Panora

59

Chief Operating Officer and President

Bonnie J. Brown

51

Chief Financial Officer, Treasurer, and Secretary

George N. Hatsopoulos

87

Director

Ahmed F. Ghoniem

62

Director

Charles T. Maxwell

82

Director

Joseph E. Aoun

61

Director

Angelina M. Galiteva, age
47, has been our Chairperson of the Board of Directors since 2005. She is founder and Chair of the Board for the Renewables 100
Policy Institute, a non-profit entity dedicated to the global advancements of renewable energy solutions since 2008. Ms. Galiteva
is also Chairperson at the World Council for Renewable Energy (WCRE) which focuses on the development of legislative and policy
initiatives to facilitate the introduction and growth of renewable energy technologies since 2003. Since 2011, Ms. Galiteva has
served on the Board of Governors of the California Independent System Operator (CA ISO), providing direction and oversight for
the California ISO which operates the California electricity grid. Also, Ms. Galiteva is a principal at New Energy Options, Inc.,
a company focusing on advancing the integration of sustainable energy solutions since 2006. Ms. Galiteva has also been a strategic
consultant with Renewable Energy Policy and Strategy Consulting since 2004. Ms. Galiteva holds a Master’s degree in Environmental
and Energy Law, a law degree from Pace University School of Law, and a bachelor’s degree from Sofia University in Bulgaria.

Our Board of Directors has determined that
Ms. Galiteva’s prior experience in the energy field qualifies her to be a member of the Board of Directors in light of the
Company’s business and structure.

John N. Hatsopoulos ,
age 80, has been the Chief Executive Officer of the Company since the organization of the Company in 2000. He has also
been the Chief Executive Officer of American DG Energy Inc., (NYSE MKT: ADGE), a publicly traded company in the On-Site Utility
business since 2000, and the Chairman of EuroSite Power Inc., a subsidiary of American DG Energy Inc. since 2009. Mr. Hatsopoulos
is a co-founder of Thermo Electron Corporation, which is now Thermo Fisher Scientific (NYSE: TMO), and the retired President and
Vice Chairman of the Board of Directors of that company. He is a member of the Board of Directors of Ilios Inc., GlenRose Instruments
Inc., Agenus Inc. (NASDAQ: AGEN), American CareSource Holdings, Inc. (NASDAQ: ANCI) and TEI Biosciences Inc., and is a former
Member of the Corporation of Northeastern University. The Company, American DG Energy Inc., EuroSite Power Inc., and GlenRose
Instruments Inc., are affiliated companies by virtue of common ownership. Mr. Hatsopoulos graduated from Athens College in Greece,
and holds a bachelor’s degree in history and mathematics from Northeastern University, as well as honorary doctorates in
business administration from Boston College and Northeastern University.

Mr. Hatsopoulos is the Company’s Chief
Executive Officer and is also the Chief Executive Officer of American DG Energy and the Chairman of GlenRose Instruments. On average,
Mr. Hatsopoulos spends approximately 50% of his business time on the affairs of the Company; however such amount varies widely
depending on the needs of the business and is expected to increase as the business of the Company develops.

Our Board of Directors has determined that
Mr. Hatsopoulos’ prior experience as co-founder, president and Chief Financial Officer of Thermo Electron Corporation, where
he demonstrated leadership capability and gained extensive expertise involving complex financial matters, and his extensive knowledge
of complex financial and operational issues qualify him to be a member of the Board of Directors in light of the Company’s
business and structure.

57

Robert A. Panora, age
59, has been our Chief Operating Officer and President since the organization of the Company in 2000 and the Chief Operating Officer
of Ilios since its inception in 2009. He had been General Manager of Tecogen’s Product Group since 1990 and Manager of Product
Development, Engineering Manager, and Operations Manager of the Company since 1984. Over his 27-year tenure with Tecogen, Mr. Panora
has been responsible for sales and marketing, engineering, service, and manufacturing. Mr. Panora contributed to the development
of Tecogen’s first product, the CM-60 cogeneration system, and was Program Manager for the cogeneration and chiller projects
that followed. Mr. Panora has had considerable influence on many aspects of Tecogen’s business, from building the employee
team, to conceptualizing product designs and authoring many of the original business documents, sales tools, and product literature
pieces. Mr. Panora has a bachelor’s and master’s degrees in Chemical Engineering from Tufts University.

Bonnie J. Brown, age
51, has been our Chief Financial Officer since 2007, our Secretary since 2010 and our Treasurer as of January 1, 2013. Ms. Brown
joined the Company in 2005 as Controller. She has also been the Chief Financial Officer of Ilios Inc. since its inception in 2009.
Prior to joining Tecogen, Ms. Brown was a partner at Sullivan Bille PC, a regional accounting firm, for 15 years where she provided
financial, accounting, audit, tax, and business consulting services for mid-sized companies. Ms. Brown has also worked at
Enterprise Bank and Trust (NASDAQ:EBTC) as project manager for special assignments including branch acquisitions and information
systems transitions in the trust department eventually serving as Internal Audit Director, establishing an in-house audit function.
She has also provided independent contractor services for a wide variety of publicly traded and closely held companies, including
consulting, internal control and Sarbanes-Oxley compliance services. Ms. Brown is a CPA and holds a B.S. in Accountancy from Bentley
College and an M.S. in Computer Information Systems from Boston University.

George N. Hatsopoulos,
age 87, has been a member of our Board since the organization of the Company in 2000. He is the founder and Chief Executive Officer
of Pharos, LLC, an organization devoted to the creation of leading edge business ventures and he is a former member of the Board
of Directors of American DG Energy Inc., an affiliated company by virtue of common ownership. He is the founder and chairman emeritus
of Thermo Electron Corporation and served as Chairman and Chief Executive Officer since its founding in 1956 until his retirement
from those positions in 1999. Dr. Hatsopoulos has served on the board of the Federal Reserve Bank of Boston, including a term as
chairman. He was a member of the Securities and Exchange Commission Advisory Committee on Capital Formation and Regulatory Process,
the Advisory Committee of the U.S. Export-Import Bank, and the boards of various corporations and institutions. Dr. Hatsopoulos
is a fellow of the American Academy of Arts and Sciences, the American Society of Mechanical Engineers and other scientific and
technical organizations. He is the recipient of numerous honors and awards in engineering, science, industry and academics, has
authored over 60 articles in professional journals, and is the principal author of textbooks on thermodynamics and thermionic energy
conversion. Dr. Hatsopoulos has been a faculty member and senior lecturer at Massachusetts Institute of Technology and continues
his association with MIT as a Life Member of the Corporation. Dr. Hatsopoulos holds bachelors, masters and doctorate degrees from
MIT, all in mechanical engineering.

Our Board of Directors has determined that
Dr. Hatsopoulos’ prior experience as founder, Chairman and Chief Executive Officer of Thermo Electron Corporation, where
he demonstrated leadership capability and gained extensive expertise involving complex financial matters, and his extensive knowledge
of complex financial and operational issues qualify him to be a member of the Board of Directors in light of the Company’s
business and structure.

Ahmed H. Ghoniem, age
62, has been a member of our Board since 2008. He is the Ronald C. Crane Professor of Mechanical Engineering at MIT. He is also
the director of the Center for 21st Century Energy, and the head of Energy Science and Engineering at MIT, where he plays a leadership
role in many energy-related activities, initiatives and programs. Mr. Ghoniem joined MIT as an assistant professor in 1983. He
is an associate fellow of the American Institute of Aeronautics and Astronautics, and Fellow of American Society of Mechanical
Engineers. Recently, he was granted the KAUST Investigator Award. He is a member of the Board of Directors of EuroSite Power Inc.,
and Ilios Inc., which are affiliated companies by virtue of common ownership. Mr. Ghoniem holds a Ph.D. in Mechanical Engineering
from the University of California, Berkeley, and an M.S. and B.S. in Mechanical Engineering from Cairo University.

58

Our Board of Directors has determined that
Dr. Ghoniem’s prior experience as a Professor of Mechanical Engineering at MIT and his prior experience in the energy sector
qualify him to be a member of our Board of Directors in light of our business and structure.

Charles T. Maxwell, age 82,
has been a member of our Board since 2001. He is a widely recognized expert in the energy sector, with over 40 years of experience
with major oil companies and investment banking firms. From 1999, until his retirement in 2012, Mr. Maxwell was a Senior Energy
Analyst with Weeden & Co. of Greenwich, Connecticut, since 1999, where he develops strategic data and forecasts on oil, gas,
and power markets. Mr. Maxwell is a member of the Board of Directors of American DG Energy, an affiliated company by virtue of
common ownership. Since the early 1980s, he has been an active member of an Oxford-based organization comprised of present or
past OPEC-county oil ministers and other oil industry executives from 30 countries who meet twice annually to analyze trends in
global energy markets. He is a member of the board of directors of Daleco Resources Corporation (OTCQB: DLOV) and Lescarden Inc.
(OTC: LCAR). Mr. Maxwell holds a bachelor’s degree in political science from Princeton University and holds a B.A. from
Oxford University as a Marshall Scholar in Middle East literature and history.

Our Board of Directors has determined
that Mr. Maxwell’s prior experience in the energy sector and his extensive experience as a director of public companies qualifies
him to be a member of the Board of Directors in light of the Company’s business and structure.

Joseph E. Aoun, age
61, has been a member of our Board since 2011. He has been President of Northeastern University since 2006. President Aoun is recognized
as a leader in higher education policy and serves on the board of directors of the American Council on Education as well as the
Boston Private Industry Council, Boston World Partnerships, Jobs for Mass, and the New England Council. He is a member of the Executive
Committee of the Greater Boston Chamber of Commerce, a member of the Massachusetts Business Roundtable and Massachusetts Math &
Science Initiative, and serves on the Leadership Council for the Mass Life Sciences Collaborative and as co-chair of the City to
City Boston initiative. President Aoun is the recipient of numerous honors and awards and is an internationally known scholar in
linguistics. President Aoun holds a master’s degree in Oriental Languages and Literature from Saint Joseph University, Beirut,
Lebanon, Diploma of Advanced Study General and Theoretical Linguistics, University of Paris VIII, Paris, France, and a Ph.D. Linguistics
and Philosophy from MIT.

Our Board of Directors has determined that
Dr. Aoun’s prior experience as the President of Northeastern University and his prior experience in the energy sector qualify
him to be a member of our Board of Directors in light of our business and structure.

Each executive officer is elected or appointed
by, and serves at the discretion of, our Board of Directors. The elected officers of the Company will hold office until their
successors are duly elected and qualified, or until their earlier resignation or removal.

Family Relationships

There are no family relationships among
members of our Board of Directors and executive officers other than George N. Hatsopoulos and John N. Hatsopoulos, who are brothers.

Board Composition

The number of directors of the Company
is established by the Board of Directors in accordance with our bylaws. The exact number of directors is currently set at six by
resolution of the Board of Directors. The directors are elected to serve for one year terms, with the term of directors expiring
each year at the annual meeting of stockholders; provided further, that the term of each director shall continue until the election
and qualification of a successor and be subject to such director’s earlier death, resignation or removal.

59

Our certificate of incorporation and
bylaws provide that the authorized number of directors may be changed only by resolution of the Board of Directors, and also provide
that our directors may be removed only for cause by the affirmative vote of the holders of at least two-thirds of the votes that
all our stockholders would be entitled to cast in an annual election of directors, and that any vacancy on our Board of Directors,
including a vacancy resulting from an enlargement of our Board of Directors, may be filled only by vote of a majority of our directors
then in office.

We have no formal policy regarding
board diversity. Our priority in selection of board members is identification of members who will further the interests of our
stockholders through his or her established record of professional accomplishment, the ability to contribute positively to the
collaborative culture among board members, knowledge of our business, and understanding of the competitive landscape.

Board Committees

Our Board of Directors directs the
management of our business and affairs and conducts its business through meetings of the Board of Directors and our committees:
the Audit Committee, the Compensation Committee, and the Nominating and Corporate Governance Committee.

The members of the Audit Committee
are Dr. Ghoniem, Ms. Galiteva, and Mr. Maxwell. The members of the Compensation Committee are Dr. Aoun, Ms. Galiteva, and Dr. Ghoniem.
The members of our Nominating and Corporate Governance Committee are Dr. Aoun, Dr. Ghoniem and Mr. Maxwell. All committee members
have been determined to be independent by our Board of Directors in accordance with the rules of the NASDAQ Capital Market rules.
The Board of Directors has also determined that Mr. Maxwell qualifies as an Audit Committee financial expert. In addition, from
time to time, other committees may be established under the direction of the Board of Directors when necessary to address specific
issues.

The functions of the Audit Committee
include reviewing and supervising the financial controls of the Company; appointing, compensating, and overseeing the work of the
independent auditors; reviewing the books and accounts of the Company; meeting with the officers of the Company regarding the Company’s
financial controls; and making recommendations to the Board of Directors based on the findings of the independent auditors. The
charter of the Audit Committee is available on the Company’s website at www.tecogen.com.

The Compensation Committee’s
functions include reviewing with management cash and other compensation policies for employees, making recommendations to the Board
of Directors regarding compensation matters and determining compensation for the Chief Executive Officer. Our Chief Executive Officer
has been instrumental in the design and recommendation to the Compensation Committee of compensation plans and awards for our directors
and executive officers including our President, Chief Operating Officer and Chief Financial Officer. All compensation decisions
for the Chief Executive Officer and all other executive officers are reviewed and approved by the Compensation Committee, subject
to ratification by the Board of Directors. The charter of the Compensation Committee is available on the Company’s website
at www.tecogen.com.

The Nominating and Corporate Governance
Committee functions are to identify persons qualified to serve as members of the Board of Directors and to recommend to the Board
of Directors persons to be nominated by the Board of Directors for election as directors at the annual meeting of stockholders
and persons to be elected by the board to fill any vacancies. In addition, the Nominating and Corporate Governance Committee is
responsible for developing and recommending to the Board of Directors a set of corporate governance guidelines applicable to the
Company (as well as reviewing and reassessing the adequacy of such guidelines as it deems appropriate from time to time) and overseeing
the annual self-evaluation of the Board of Directors. The charter of the Nominating and Corporate Governance Committee is available
on the Company’s website at www.tecogen.com.

60

Director Compensation

Each director who is not also one of
our employees will receive a fee of $500 per day for service on those days that our Board of Directors and/or each of the Audit,
Compensation, or Nominating and Corporate Governance Committees hold meetings, or otherwise conduct business. Non-employee directors
also will be eligible to receive stock or options awards under our 2006 Stock Incentive Plan, as amended, or the Stock Plan. We
reimburse all of our non-employee directors for reasonable travel and other expenses incurred in attending Board of Directors and
committee meetings. Any director who is also one of our employees receives no additional compensation for serving as a director.
Our non-employee directors did not receive any compensation in cash prior to or during 2010. Until December 2011, the compensation
of directors was only in stock awards.

Board Leadership Structure

We separate the roles of Chief Executive
Officer and Chairman in recognition of the differences between the two roles. Our Chief Executive Officer is responsible for setting
the strategic direction for the Company and the overall leadership and performance of the Company. Our Chairman provides guidance
to the Chief Executive Officer, sets the agenda for Board of Director meetings, presides over meetings of the full Board of Directors,
and leads all executive meetings of the independent directors. We are a small company with a small management team, and we feel
the separation of these roles enhances high-level attention to our business.

Our Board of Directors’ Role in Risk Oversight

Our Board of Directors oversees our
risk management processes directly and through its committees. Our management is responsible for risk management on a day-to-day
basis. The Audit Committee assists the Board of Directors in fulfilling its oversight responsibilities with respect to risk management
in the areas of financial reporting, internal controls, and compliance with legal and regulatory requirements, and discusses policies
with respect to risk assessment and risk management, including guidelines and policies to govern the process by which the Company’s
exposure to risk is handled. The Compensation Committee assists the Board of Directors in fulfilling its oversight responsibilities
with respect to the management of risks arising from our compensation policies and programs. The Nominating and Corporate Governance
Committee assists the Board of Directors in fulfilling its oversight responsibilities with respect to the management of risks associated
with board organization, membership and structure, succession planning for our directors, and corporate governance.

Code of Business Conduct and Ethics

The Company has adopted a code of business
conduct and ethics that applies to the Company’s directors, officers, and employees. The Company’s code of business
conduct and ethics is intended to promote honest and ethical conduct, including the ethical handling of actual or apparent conflicts
of interest between personal and professional relationships; full, fair, accurate, timely and understandable disclosure in reports
and documents that the Company files with, or submits to, the SEC and in other public communications made by the Company; compliance
with applicable governmental laws, rules and regulations; prompt internal reporting of violations of the code of business conduct
and ethics to an appropriate person or persons identified in the code of business conduct and ethics; and accountability for adherence
to the code of business conduct and ethics. The Company’s code of business conduct and ethics is available on the Company’s
website at www.tecogen.com.

61

EXECUTIVE OFFICER AND DIRECTOR COMPENSATION

The Compensation Committee and Board of
Directors construct policies and guidelines regarding executive compensation. The major components of executive compensation will
be base salary, annual incentive bonuses, equity incentive awards and customary employee benefits. Among the factors likely to
be relevant are:

•

the executive officer’s skills and experience;

•

the particular importance of the executive officer’s position to us;

•

the executive officer’s individual performance;

•

the executive officer’s growth in his or her position; and

•

base salaries for comparable positions within our Company and at other companies.

Our Compensation Committee performs evaluations
of our executive officers’ compensation at least annually and may solicit the input of a compensation consulting firm and
peer group benchmarking data in making any adjustments believed to be appropriate.

The following table sets forth information
with respect to the compensation of our executive officers for the Company's last two completed fiscal years:

Summary Compensation Table

Name and principal position

Year

Salary ($)

Bonus ($)

Stock awards ($)

Option awards ($)(1)

All other compensation
($)

Total ($)

John N. Hatsopoulos

2013

1

—

—

—

—

1

Chief Executive Officer

2012

1

—

—

—

—

1

(Principal Executive Officer)

Robert A. Panora (2)

2013

163,770

—

—

—

1,032

164,802

Chief Operating Officer and President

2012

163,770

—

—

—

1,032

164,802

Bonnie J. Brown (3)

2013

156,000

—

—

—

360

156,360

Chief Financial Officer, Treasurer and Secretary

2012

156,000

—

—

—

360

156,360

(Principal Financial Officer)

Anthony S. Loumidis (4)

Former Vice President and Treasurer

2012

25,091

25,091

(1)

The amounts in the “Stock Option Awards” column reflect the aggregate grant date fair value of the awards computed
in accordance with FASB ASC Topic 718. The assumptions used by us with respect to the valuation of stock and option awards are
set forth in Note 10 – Stockholders’ equity to our financial statements included elsewhere in this registration
statement.

(2)

Includes group life insurance of $1,032 for 2013 and 2012, respectively.

(3)

Includes group life insurance of $360 for 2013 and 2012.

(4)

Mr. Loumidis resigned as Vice President and Treasurer of the Company effective December 31, 2012.

62

Outstanding Equity Awards at Fiscal Year-End

The following table sets forth information
with respect to outstanding equity awards held by our executive officers as of December 31, 2013:

Option awards

Stock awards

Name

Number of
securities underlying unexercised options (#) exercisable

Number of
securities underlying unexercised options (#) unexercisable

Option
exercise price ($)

Option
expiration date

Number of
shares of stock that have not vested (#)

Market value

of shares

of stock

that have

not vested ($)(1)

John N. Hatsopoulos

—

—

—

—

—

—

Robert A. Panora (2)(3)

62,500

62,500

2.60

2/14/2021

138,350

622,575

Bonnie J. Brown (4)(5)

25,000

—

1.20

2/13/2015

12,500

56,250

Bonnie J. Brown (6)

50,000

—

2.00

3/11/2019

—

—

Bonnie J. Brown (7)

18,750

6,250

2.60

2/18/2020

—

—

(1)

Market value of shares of stock that have not vested is computed on the last private placement price of the Company’s
Common Stock on January 17, 2014, which was $4.50 per share.

(2)

Includes stock option award granted on February 15, 2011, with 25% of the shares vesting on February 15, 2012 and then an additional
25% of the shares vesting on each of the subsequent three anniversaries, subject to Mr. Panora’s continued employment and
subject to acceleration of vesting upon a change in control.

(3)

Includes 138,350 shares of restricted Common Stock at a purchase price of $.001 per share granted on December 4, 2006, with
100% of the shares vesting one year after the Company’s initial public offering, subject to acceleration of vesting upon
a change in control prior to a termination event.

(4)

Includes stock option award granted on February 13, 2008, with 25% of the shares vesting on February 13, 2009 and then an additional
25% of the shares vesting on each of the subsequent three anniversaries, subject to Ms. Brown’s continued employment and
subject to acceleration of vesting upon a change in control.

(5)

Includes 12,500 shares of restricted Common Stock at a purchase price of $.004 per share granted on December 13, 2006, with
100% of the shares vesting one year after the Company’s initial public offering, subject to acceleration of vesting upon
a change in control prior to a termination event.

(6)

Includes stock option award granted on March 11, 2009, with 25% of the shares vesting on March 11, 2010 and then an additional
25% of the shares vesting on each of the subsequent three anniversaries, subject to Ms. Brown’s continued employment and
subject to acceleration of vesting upon a change in control.

(7)

Includes stock option award granted on February 28, 2010, with 25% of the shares vesting on February 28, 2011 and then an additional
25% of the shares vesting on each of the subsequent three anniversaries, subject to Ms. Brown’s continued employment and
subject to acceleration of vesting upon a change in control.

Director Compensation

Each director who is not also one of our
employees will receive a fee of $500 per day for service on those days that our Board of Directors and or each of the Audit, Compensation
or Nominating and Corporate Governance Committees hold meetings, or otherwise conduct business. Non-employee directors also will
be eligible to receive stock or option awards under our equity incentive plan. We reimburse all of our non-employee directors for
reasonable travel and other expenses incurred in attending Board and committee meetings. Any director who is also one of our employees
receives no additional compensation for serving as a director.

63

The following table sets forth information
with respect to the compensation of our directors as of December 31, 2013:

Name

Fees
earned or paid in cash ($)

Stock
awards ($)

Option
awards ($)

All
other compensation ($)

Total
($)

Angelina M. Galiteva

1,500

—

—

—

1,500

John N. Hatsopoulos

—

—

—

—

—

George N. Hatsopoulos

—

—

—

—

—

Ahmed F. Ghoniem

500

—

—

—

500

Charles T. Maxwell

1,000

—

—

—

1,000

Joseph E. Aoun

—

—

—

—

—

Outstanding Equity Awards at Fiscal Year-End Table

The following table summarizes the outstanding
equity awards held by each director as of December 31, 2013:

Option awards

Stock awards

Name

Number of
securities underlying unexercised options (#) exercisable

Number of
securities underlying unexercised options (#) unexercisable

Option
exercise price ($)

Option
expiration date

Number of
shares of stockthat have not vested (#)

Market value
of shares of stock that have not vested ($)(1)

Angelina M. Galiteva (2)(3)

12,500

12,500

2.60

2/14/2021

25,000

112,500

John N. Hatsopoulos

—

—

—

—

—

—

George N. Hatsopoulos

—

—

—

—

—

—

Ahmed F. Ghoniem (4)(5)

12,500

12,500

2.60

2/14/2021

25,000

112,500

Charles T. Maxwell (6)(7)

12,500

12,500

2.60

2/14/2021

25,000

112,500

Joseph E. Aoun (8)

—

25,000

4.50

12/31/2023

—

—

(1)

Market value of shares of Common Stock that have not vested is computed by the Company’s most recent private placement
of Common Stock on January 17, 2014, which was $4.50 per share.

(2)

Includes 25,000 shares of restricted Common Stock at a purchase price of $.004 per share granted on December 13, 2006, with
100% of the shares vesting one year after the Company’s initial public offering.

(3)

Includes stock option award granted on February 15, 2011, with 25% of the shares vesting on February 15, 2012, and then an
additional 25% of the shares vesting on each of the subsequent three anniversaries, provided that Ms. Galiteva serves as a director
or consultant to the Company.

(4)

Includes stock option award granted on February 15, 2011, with 25% of the shares vesting on February 15, 2012, and then an
additional 25% of the shares vesting on each of the subsequent three anniversaries, provided that Mr. Ghoniem serves as a director
or consultant to the Company.

(5)

Includes 25,000 shares of restricted Common Stock at a purchase price of $.004 per share granted on October 1, 2008, with 100%
of the shares vesting 180 days after the Company’s initial public offering.

(6)

Includes stock option award granted on February 15, 2011, with 25% of the shares vesting on February 15, 2012, and then an
additional 25% of the shares vesting on each of the subsequent three anniversaries, provided that Mr. Maxwell serves as a director
or consultant to the Company.

64

(7)

Includes 25,000 shares of restricted Common Stock at a purchase price of $.004 per share granted on October 1, 2008, with 100%
of the shares vesting 180 days after the Company’s initial public offering.

(8)

Includes stock option award granted on December 31, 2013, with 25% of the shares vesting on December 31, 2014, and then an
additional 25% of the shares vesting on each of the subsequent three anniversaries, provided that Dr. Aoun serves as a director
or consultant to the Company.

There have been no other stock awards granted to
date and none of such options have been exercised.

2006 Stock Incentive Plan

The Company’s 2006 Stock Incentive
Plan, or Stock Plan, provides for the grant of stock-based awards to employees, officers and directors of, and consultants or advisors
to, the Company and any of its present or future parents, subsidiaries or affiliates. The Stock Plan is included as Exhibit 10.1
hereto.

Under the Stock Plan, the Company may grant
stock options, restricted stock and other stock-based awards. As of December 31, 2013, a total of 1,148,000 shares of Common
Stock may be issued upon the exercise of options or other awards granted under the Stock Plan.

The Stock Plan is administered by the Board
of Directors and the Compensation Committee. Subject to the provisions of the Stock Plan, the Board of Directors and the Compensation
Committee each has the authority to select the persons, to whom awards are granted and determine the terms of each award, including
the number of shares of Common Stock subject to the award. Payment of the exercise price of an award may be made in cash, in a
“cashless exercise” through a broker, or if the applicable stock option agreement permits, shares of Common Stock or
by any other method approved by the Board of Directors or Compensation Committee. Unless otherwise permitted by the Company, awards
are not assignable or transferable except by will or the laws of descent and distribution.

Upon the consummation of an acquisition
of the business of the Company, by merger or otherwise, the Board of Directors shall, as to outstanding awards (on the same basis
or on different bases as the Board of Directors shall specify), make appropriate provision for the continuation of such awards
by the Company or the assumption of such awards by the surviving or acquiring entity and by substituting on an equitable basis
for the shares then subject to such awards either (a) the consideration payable with respect to the outstanding shares of
Common Stock in connection with the acquisition, (b) shares of stock of the surviving or acquiring corporation or (c) such
other securities or other consideration as the Board of Directors deems appropriate, the fair market value of which (as determined
by the Board of Directors in its sole discretion) shall not materially differ from the fair market value of the shares of Common
Stock subject to such awards immediately preceding the acquisition. In addition to or in lieu of the foregoing, with respect to
outstanding stock options, the Board of Directors may, on the same basis or on different bases as the Board of Directors shall
specify, upon written notice to the affected optionees, provide that one or more options then outstanding must be exercised, in
whole or in part, within a specified number of days of the date of such notice, at the end of which period such options shall terminate,
or provide that one or more options then outstanding, in whole or in part, shall be terminated in exchange for a cash payment equal
to the excess of the fair market value (as determined by the Board of Directors in its sole discretion) for the shares subject
to such options over the exercise price thereof.

The Board of Directors may at any time provide
that any stock options shall become immediately exercisable in full or in part, that any restricted stock awards shall be free
of some or all restrictions, or that any other stock-based awards may become exercisable in full or in part or free of some or
all restrictions or conditions, or otherwise realizable in full or in part, as the case may be.

The Board of Directors or Compensation Committee
may, in its sole discretion, amend, modify or terminate any award granted or made under the Stock Plan, so long as such amendment,
modification or termination would not materially and adversely affect the participant.

65

Securities Authorized for Issuance Under Equity Compensation
Plans

The following table provides information
as of December 31, 2013, regarding Common Stock that may be issued under the Company’s equity compensation plans.

Plan category

Number of securities to be issued upon exercise of outstanding options, warrants and rights

Number of securities remaining available for future issuance under equity compensation plans (excluding securities reflected in second column)

Equity compensation plans approved by security holders

1,148,000

$

2.13

58,683

Equity compensation plans not approved by security holders

—

—

—

Total

1,148,000

$

2.13

58,683

In February 2011, our management conducted
an assessment of the risks associated with our compensation policies and practices. This process included a review of our compensation
programs, a discussion of the types of practices that could be reasonably likely to create material risks, and an analysis of the
potential effects on the Company on related risks as a whole.

Although we reviewed all of our compensation
programs, we paid particular attention to programs involving incentive-based payouts and programs that involve our executive officers.
During the course of our assessment, we consulted with the Compensation Committee of our Board of Directors.

We believe that our compensation programs
are designed to create appropriate incentives without encouraging excessive risk taking by our employees. In this regard, our compensation
structure contains various features intended to mitigate risk. For example:

A portion of the compensation package for our sales-based employees consists of commissions for shares sold and installed,
which package is designed to link an appropriate portion of compensation to long-term performance, while providing a balanced compensation
model overall.

•

The Compensation Committee oversees our compensation policies and practices and is responsible for reviewing and approving
executive compensation, annual incentive compensation plans applicable to sales employees and other compensation plans.

Our Compensation Committee, in its
evaluation, determined that it does not believe that the Company employs any compensation plans or practices that create incentives
for employees to deliver short-term profits at the expense of generating systematic risks for the Company. Based on this and the
assessment described above, we have concluded that the risks associated with our compensation policies and practices are not reasonably
likely to have material adverse effect on the Company.

Compensation Committee Interlocks and Insider Participation

None of our executive officers serve as
a member of the board of directors or compensation committee, or other committee serving an equivalent function, of any other entity
that has one or more of its executive officers serving as a member of our Board of Directors or Compensation Committee. None of
the current members of the Compensation Committee of our Board of Directors has ever been one of our employees.

66

Employment Contracts and Termination of Employment and Change-in-Control
Arrangements

None of our executive officers has an employment
contract or change-in-control arrangement, other than stock and option awards that contain certain change-in-control provisions
such as accelerated vesting due to acquisition. In the event an acquisition that is not a private transaction occurs while the
optionee maintains a business relationship with the Company and the option has not fully vested, the option will become exercisable
for 100% of the then number of shares as to which it has not vested and such vesting to occur immediately prior to the closing
of the acquisition.

The stock and option awards that would vest
for each named executive if a change-in-control were to occur are disclosed under our Outstanding Equity Awards at Fiscal Year-End
Table. Specifically, as of December 31, 2013, Robert A. Panora, our Chief Operating Officer and President, had 62,500
stock options and 138,350 shares of restricted stock that had not vested and Bonnie J. Brown, our Chief Financial Officer, had
6,250 stock options and 12,500 shares of restricted stock that had not vested.

Change-in-Control shall mean (a) the acquisition
in a transaction or series of transactions by any person (such term to include anyone deemed a person under Section 13(d)(3) of
the Exchange Act), other than the Company or any of its subsidiaries, or any employee benefit plan or related trust of the Company
or any of its subsidiaries, of beneficial ownership (within the meaning of Rule 13d-3 promulgated under the Exchange Act) of 50%
or more of the combined voting power of the then outstanding voting securities of the Company entitled to vote generally in the
election of directors; provided a Change-in-Control shall not occur solely as the result of an initial public offering or (b) the
sale or other disposition of all or substantially all of the assets of the Company in one transaction or series of related transactions.

Option Awards Change-in-Control Definition

Accelerated vesting due to acquisition.
In the event an acquisition that is not a private transaction occurs while the optionee maintains a business relationship with
the Company and the option has not fully vested, the option shall become exercisable for 100% of the then number of shares as to
which it has not vested, such vesting to occur immediately prior to the closing of the acquisition.

Definitions. The following definitions
shall apply to certain terms used in this Section:

Acquisition means (i) the sale of
the Company by merger in which the stockholders of the Company in their capacity as such no longer own a majority of the outstanding
equity securities of the Company (or its successor); or (ii) any sale of all or substantially all of the assets or capital stock
of the Company (other than in a spin-off or similar transaction) or (iii) any other acquisition of the business of the Company,
as determined by the Board.

Business relationship means service
to the Company or its successor in the capacity of an employee, officer, director or consultant.

Private transaction means any acquisition
where the consideration received or retained by the holders of the then outstanding capital stock of the Company does not consist
of (i) cash or cash equivalent consideration, (ii) securities which are registered under the Securities Act, or any successor statute
or (iii) securities for which the Company or any other issuer thereof has agreed, including pursuant to a demand, to file a registration
statement within 90 days of completion of the transaction for resale to the public pursuant to the Securities Act.

67

Director Independence

Under Rule 5605(b)(1) of the Nasdaq
Marketplace Rules, independent directors must comprise a majority of a listed company’s board of directors within one year
of listing. In addition, Nasdaq Marketplace Rules require that, subject to specified exceptions, each member of a listed company’s
audit, compensation, and nominating and governance committees be independent. Audit committee members must also satisfy the independence
criteria set forth in Rule 10A-3 under the Exchange Act, and compensation committee members must also satisfy the independence
criteria set forth in Rule 10C under the Exchange Act. Under Nasdaq Marketplace Rule 5605(a)(2), a director will only qualify as
an “independent director” if, in the opinion of that company’s board of directors, that person does not have
a relationship that would interfere with the exercise of independent judgment in carrying out the responsibilities of a director.
In order to be considered to be independent for purposes of Rule 10A-3, a member of an audit committee of a listed company may
not, other than in his or her capacity as a member of the audit committee, the board of directors, or any other board committee:
(1) accept, directly or indirectly, any consulting, advisory, or other compensatory fee from the listed company or any of its subsidiaries;
or (2) be an affiliated person of the listed company or any of its subsidiaries.

Our Board of Directors intends to review
its composition, the composition of its committees and the independence of each director according to the independence standards
established by applicable SEC rules and the Nasdaq Marketplace Rules. As part of its review, our Board of Directors will consider
the relationships that each non-employee director has with our company and all other facts and circumstances our Board of Directors
deems relevant in determining their independence, including the beneficial ownership of our capital stock by each non-employee
director.

68

PRINCIPAL STOCKHOLDERS

The table below sets forth information
with respect to the beneficial ownership of our common stock as of March 31, 2014 by:

•

each of our named executive officers;

•

all of our directors and executive officers as a group; and

•

each person, or group of affiliated persons, who is known to us to beneficially own more than 5% of our outstanding shares
of Common Stock.

Except as otherwise indicated, to our
knowledge, the persons named in the table below have sole voting and investment power with respect to all shares of Common Stock
shown as beneficially owned by them, subject to community property laws, where applicable, and the address for each of the named
directors and executive officers is 45 First Avenue, Waltham, MA 02451.

The number of shares beneficially owned
by each stockholder is determined under rules promulgated by the SEC. The information does not necessarily indicate beneficial
ownership for any other purpose. Under those rules, the number of shares of Common Stock deemed outstanding includes shares issuable
upon exercise of stock options held by the respective person or group that may be exercised within 60 days. For purposes of calculating
each person’s or group’s percentage ownership, shares of Common Stock issuable pursuant to stock options exercisable
within 60 days after December 31, 2013 are reflected in the table below and included as outstanding and beneficially owned for
that person or group but are not treated as outstanding for the purpose of computing the percentage ownership of any other person
or group. The percentages of shares outstanding provided in the table are based on a total of 15,161,600 shares of our common stock
outstanding on March 31, 2014. For purposes of the table below, we have assumed shares of Common Stock will be sold by us
in this offering and all shares offered in the secondary offering will be sold by the selling stockholders.

Shares Beneficially Owned Prior to this Offering

Shares Beneficially Owned After this Offering

Directors, Executive Officers and 5% Stockholders

Number (1)

Percent

Number (1)

Percent

5% Stockholders:

John N. Hatsopoulos (1)

3,718,939

24.5

%

3,718,939

21.7

%

George N. Hatsopoulos (2)

3,554,651

23.5

%

3,554,651

20.7

%

Michaelson Capital Special Finance Fund LP (3)

1,000,001

6.4

%

1,000,001

5.8

%

RBC Cees Nominees Limited (4)

904,105

6

%

904,105

5.3

%

Joseph J. Ritchie (5)

896,613

5.9

%

896,613

5.2

%

Directors and Officers:

John N. Hatsopoulos (1)

3,718,939

24.5

%

3,718,939

21.7

%

George N. Hatsopoulos (2)

3,554,651

23.5

%

3,554,651

20.7

%

Robert A. Panora (6)

257,100

1.7

%

225,850

1.5

%

Bonnie J. Brown (7)

112,500

0.7

%

106,250

0.7

%

Charles T. Maxwell (8)

93,750

0.6

%

87,500

0.5

%

Angelina M. Galiteva (9)

68,750

0.4

%

62,500

0.4

%

Ahmed F. Ghoniem (10)

43,750

0.3

%

37,500

0.3

%

Joseph E. Aoun

—

—

—

—

All executive officers and directors as a group (8 persons)

7,849,440

51.8

%

7,849,440

45.7

%

69

(1)

Includes:(a) 2,135,210 shares of Common Stock held by J&P Enterprises LLC for the benefit of: (1) John N. Hatsopoulos and
(2) Patricia L. Hatsopoulos. John N. Hatsopoulos is the Executive Member of J&P Enterprises LLC and has voting and investment
power; (b) 593,770 shares of Common Stock held by John N. Hatsopoulos and his wife, Patricia L. Hatsopoulos, as joint tenants with
rights of survivorship, each of whom share voting and investment power; and (c) 989,859 shares of Common Stock held by The John
N. Hatsopoulos Family Trust 2007 for the benefit of: (1) Patricia L. Hatsopoulos, (2) Alexander J. Hatsopoulos, and (3) Nia Marie
Hatsopoulos, for which Dr. George N. Hatsopoulos and Ms. Patricia L. Hatsopoulos are the trustees; and (d) 100 shares of Common
Stock held by Patricia L. Hatsopoulos, John's spouse.

(2)

Includes: (a) 1,304,651 shares of Common Stock, directly held by Dr. George N. Hatsopoulos; (b) 2,250,000 shares of Common
Stock held by The Hatsopoulos Family 2012 Trust.This amount does not include (a) 234,049 shares held in the 1994 Hatsopoulos Family
Trust for the benefit of Marina Hatsopoulos Bornhorst, for which Ms. Daphne Hatsopoulos and Mr. Gordon Erhlich are the trustees.
The trusts are for the benefit of Dr. Hatsopoulos's adult children. Dr. Hatsopoulos disclaims beneficial ownership of the shares
held by this trust. The percentage of shares owned after the offering assumes that Dr. Hatsopoulos does not sell any shares in
the secondary offering.

(3)

Includes: (a) 444,445 shares of Common Stock purchased December 23, 2013; and (b) 555,556 shares of Common Stock issuable upon
conversion of $3,000,000 principal amount of 4% convertible debentures.

(4)

Includes 904,105 shares of Common Stock purchased in August 2010 and November 2011 held by RBC cees Nominees Ltd. The address
of RBC cees Nominees Ltd. is 19-21 Broad Street, St. Hellier, Jersey JE1 3PB, Channel Islands.

(5)

Includes 896,613 shares of Common Stock, directly held by Mr. Ritchie. The address of Mr. Ritchie is 2100 Enterprise Avenue,
Geneva, IL 60134.

(6)

Includes: (a) 163,350 shares of Common Stock, directly held by Mr. Panora, and (b) options to purchase 93,750 shares of Common
Stock exercisable within 60 days of March 31, 2014.

(7)

Includes: (a) 12,500 shares of Common Stock, directly held by Ms. Brown, and (b) options to purchase 100,000 shares of Common
Stock exercisable within 60 days of March 31, 2014.

(8)

Includes: (a) 75,000 shares of Common Stock, directly held by Mr. Maxwell, and (b) options to purchase 18,750 shares of Common
Stock exercisable within 60 days of March 31, 2014.

(9)

Includes: (a) 50,000 shares of Common Stock, directly held by Ms. Galiteva and (b) options to purchase 18,750 shares of Common
Stock exercisable within 60 days of March 31, 2014.

(10)

Includes: (a) 25,000 shares of Common Stock, directly held by Mr. Ghoniem, and (b) options to purchase 18,750 shares of Common
Stock exercisable within 60 days of March 31, 2014.

70

CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS

The Company has five affiliated companies:
(a) American DG Energy, a publicly traded company that distributes, owns and operates on-site energy systems that produce electricity,
hot water, heat, and cooling in the United States; (b) EuroSite Power, a publicly traded company that distributes, owns, and operates
on-site energy systems that produce electricity, hot water, heat, and cooling in the United Kingdom and Europe; (c) GlenRose Instruments,
a company that provides radiological services, operates a radiochemistry laboratory network, and provides radiological characterization
and analysis, hazardous, radioactive, and mixed waste management, facility, environmental, safety, and industrial hygiene health
management; (d) Pharos, a private company that offers investment services in the healthcare sector; and (e) Levitronix Technologies
LLC, or Levitronix, a worldwide leader in magnetically levitated bearingless motor technology, specializing in supplying medical
blood pumps to the medical community and ultra-pure fluid handling devices for microelectronics, life science, and industrial applications.

These companies are affiliates because several
of the major stockholders of those companies have a significant ownership position in the Company. American DG Energy, EuroSite
Power, GlenRose Instruments, Pharos, and Levitronix do not own any shares of the Company, and the Company does not own any shares
of American DG Energy, EuroSite Power, GlenRose Instruments, Pharos, or Levitronix. The businesses of GlenRose Instruments, Pharos,
and Levitronix are not related to the business of the Company.

American DG Energy, EuroSite Power, GlenRose
Instruments, Pharos and Levitronix are affiliated companies by virtue of common ownership. The common stockholders include:

•

John N. Hatsopoulos, the Company’s Chief Executive Officer who is also: (a) the Chief Executive Officer and a director
of American DG Energy and holds 10.7% of the company’s common stock; (b) the Chairman of EuroSite Power; (c) a director of
Ilios and holds 7.2% of the company’s common stock; and (d) the Chairman of GlenRose Instruments and holds 15.7% of the company’s
common stock.

•

Dr. George N. Hatsopoulos, who is John N. Hatsopoulos’ brother, and is also: (a) a director of American DG Energy and
holds 13.6% of the company’s common stock; (b) an investor in Ilios and holds 3.1% of the company’s common stock; (c)
an investor of GlenRose Instruments and holds 15.7% of the company’s common stock; (d) an investor of Pharos and may be deemed
to hold 24.4% of the company’s common stock; and (e) a director and an investor of Levitronix and may be deemed to hold 21.4%
of the company’s common stock.

Additionally, the following related persons
had or may have a direct or indirect material interest in our transactions with our affiliated companies:

•

Barry J. Sanders, who is: (a) the President and Chief Operating Officer of American DG Energy, (b) the Chief Executive Officer
and a director of EuroSite Power and (c) the Chairman of Ilios.

•

Anthony S. Loumidis, the Company’s former Vice President and Treasurer who is: (a) the former Chief Financial Officer
Secretary and Treasurer of American DG Energy, (b) the former Chief Financial Officer Secretary and Treasurer of EuroSite Power,
(c) the former Chief Financial Officer Secretary and Treasurer of GlenRose Instruments and (d) the former Treasurer of Ilios.

American DG Energy has sales representation
rights to the Company’s products and services in New England. Revenue from sales of cogeneration and chiller systems, parts
and service to American DG Energy during the years ended December 31, 2013 and 2012 amounted to $758,930 and $3,795,666, respectively.

On October 20, 2009, American DG Energy,
in the ordinary course of its business, signed a Sales Representative Agreement with Ilios to promote, sell and service the Ilios
high-efficiency heating products, such as the high efficiency water heater, in the marketing territory of the New England states,
including Connecticut, Rhode Island, Massachusetts, New Hampshire, Vermont, and Maine. The marketing territory also includes all
of the nations in the European Union. The initial term of this Agreement is for five years, after which it may be renewed for successive
one-year terms upon mutual written agreement. American DG Energy has not yet sold any products under this agreement and therefore,
no amounts have been required to be paid.

71

On September 24, 2001, the Company entered
into subscription agreements with investors for the sale of convertible debentures. The primary investors were George N. Hatsopoulos,
who subscribed for debentures having an initial principal amount of $200,000; the John N. Hatsopoulos 1989 Family Trust for the
benefit of Nia Marie Hatsopoulos, or the Nia Hatsopoulos Trust, which subscribed for debentures having an initial principal amount
of $50,000; and the John N. Hatsopoulos 1989 Family Trust for the benefit of Alexander John Hatsopoulos, or the Alexander Hatsopoulos
Trust, which subscribed for debentures having an initial principal amount of $50,000. Nia Hatsopoulos and Alexander Hatsopoulos
are John N. Hatsopoulos’ adult children. John N. Hatsopoulos disclaims beneficial ownership of the shares held by these trusts.
The debentures accrue interest at a rate of 6% per annum and were due on September 24, 2007. The debentures are convertible, at
the option of the holder, into shares of Common Stock at a conversion price of $1.20 per share.

On September 24, 2007, George N. Hatsopoulos,
the Nia Hatsopoulos Trust and the Alexander Hatsopoulos Trust, holding debentures representing a majority of the then-outstanding
principal amount of the debentures, agreed to extend the debenture term to September 24, 2011.

On May 11, 2009, George N. Hatsopoulos converted
$109,033 of the principal amount under the debentures held by him, together with accrued interest in the amount of $90,967 into
400,000 shares of Common Stock of Ilios, the Company’s then newly-formed subsidiary, which were previously held by the Company,
at a conversion price of $0.50 per share. The difference between the Company’s purchase price of the Ilios shares and the
amount of debt forgiveness was recorded as additional paid-in capital.

On September 30, 2009, Joseph J. Ritchie
elected to convert the outstanding principal amount under the debenture held by him, $30,000, together with accrued interest of
$14,433, into 37,028 shares of the Company’s Common Stock at a conversion price of $1.20 per share.

On September 24, 2011, George N. Hatsopoulos,
the Nia Hatsopoulos Trust and the Alexander Hatsopoulos Trust, holding debentures representing a majority of the then-outstanding
principal amount of the debentures, agreed to extend the term of the debentures to September 24, 2013 and requested that accrued
interest in the aggregate amount of approximately $72,960 be converted into the Company’s Common Stock at $2.00 per share
(which was the average price of the Company’s stock between September 24, 2001 and September 24, 2011). As a result, the
Company issued 6,474 shares of Common Stock to George N. Hatsopoulos, 15,003 shares of Common Stock to the Nia Hatsopoulos Trust
and 15,003, shares of Common Stock to the Alexander Hatsopoulos Trust.

On September 30, 2012, the remaining principal
amount under the debentures held by the Nia Hatsopoulos Trust and the Alexander Hatsopoulos Trust, including the applicable accrued
interest, was converted into 42,620 shares of Common Stock issued to each of the Nia Hatsopoulos Trust and the Alexander Hatsopoulos
Trust.

On September 20, 2013, the term of the debentures
held by George N. Hatsopoulos was extended to October 31, 2013. On October 18, 2013, George N. Hatsopoulos elected to convert the
outstanding principal balance of the debenture held by him of $90,967 into 75,806 shares of the Company’s Common Stock at
a conversion price of $1.20 per share. In addition, Mr. Hatsopoulos requested that the accrued interest earned in 2012 in the amount
of $6,913 be converted into 2,161 shares of the Company’s Common Stock at a conversion price of $3.20 per share and that
the accrued interest earned on or after January 1, 2013 in the amount of $4,366 be converted into 970 shares of the Company’s
Common Stock at a conversion price of $4.50 per share.

72

On May 11, 2009, John Hatsopoulos converted
an aggregate of $427,432 in principal amount under demand notes held by him, together with accrued interest in the amount of $72,568
into 1,000,000 shares of Common Stock of Ilios, which were previously held by the Company, at a conversion price of $0.50 per share.
The difference between the Company’s purchase price of the Ilios shares and the amount of debt forgiveness was recorded as
additional paid-in capital.

On September 10, 2008, the Company entered
into a demand note agreement with John N. Hatsopoulos in the principal amount of $250,000 at an annual interest rate of 5%. On
September 7, 2011, the Company entered into an additional demand note agreement with John N. Hatsopoulos, in the principal amount
of $750,000 at an annual interest rate of 6%. On November 30, 2012, the Company entered into an additional demand note agreement
with John N. Hatsopoulos in the principal amount of $300,000 at an annual interest rate of 6%. On October 3, 2013, the Company
signed a demand note for $450,000, which accrues interest at 6%, to John N. Hatsopoulos, the Company’s Chief Executive Officer.
Unpaid principal and interest on the demand notes are due upon demand. On January 6, 2014 these demand notes were paid in full
with accrued interest.

On March 25, 2013, the Company entered into
a Revolving Line of Credit Agreement, or the Credit Agreement, with John N. Hatsopoulos, our Chief Executive Officer. Under the
terms of the Credit Agreement, as amended on August 13, 2013, Mr. Hatsopoulos has agreed to lend the Company up to an aggregate
of $1,500,000 from time to time, at the written request of the Company. Any amounts borrowed by the Company pursuant to the Credit
Agreement will bear interest at the Bank Prime Rate as quoted from time to time in the Wall Street Journal plus 1.5% per year.
Repayment of the principal amount borrowed pursuant to the Credit Agreement will be due on March 1, 2014. In addition, the company
may prepay accrued interest, provided that prepayment may not be made prior to January 1, 2014. As of December 31, 2013 the
Company has borrowed $1,200,000 pursuant to the Credit Agreement. On January 6, 2014, the Company repaid the then outstanding principal
balance of $1,200,000 together with accrued interest of $25,347.

If the Company’s existing resources,
including cash and cash equivalents and future cash flows from operations are not sufficient to meet the working capital requirements
of the Company’s existing business through 2014, John Hatsopoulos has committed to provide any shortfall in the form of a
demand note.

On March 26, 2014, the Company entered into
a Revolving Line of Credit Agreement, or the 2014 Credit Agreement, with John N. Hatsopoulos, our Chief Executive Officer. Under
the terms of the 2014 Credit Agreement, Mr. Hatsopoulos has agreed to lend the Company up to an aggregate of $3,500,000 from time
to time, at the written request of the Company. Any amounts borrowed by the Company pursuant to the 2014 Credit Agreement
will bear interest at the Bank Prime Rate as quoted from time to time in the Wall Street Journal plus 1.5% per year. Repayment
of the principal amount borrowed pursuant to the 2014 Credit Agreement will be due on March 25, 2015.

For additional disclosure on the Company’s
debt see Note 7 – Demand notes payable, convertible debentures and line of credit – related party.

John N. Hatsopoulos’ salary is $1.00
per year. On average, Mr. Hatsopoulos spends approximately 50% of his business time on the affairs of the Company; however such
amount varies widely depending on the needs of the business and is expected to increase as the business of the Company develops.

On July 1, 2012 the Company signed a Facilities
and Support Services Agreement, or the Facilities and Support Services Agreement, with American DG Energy for a period of one year,
renewable annually, on July 1st, by mutual agreement. Under this agreement, the Company provides American DG Energy with certain
office and business support services and also provides pricing based on a volume discount depending on the level of American DG
Energy purchases of cogeneration and chiller products. For certain sites, American DG Energy hires the Company to service its chiller
and cogeneration products. The Company also provides office space and certain utilities to American DG Energy based on a monthly
rate set at the beginning of each year. Also, under this agreement, American DG Energy has sales representation rights to the Company's
products and services in New England.

73

On July 1, 2013 the Company entered into
the First Amendment to the Facilities, Support Services and Business Agreement, or the First Amendment, with American DG Energy.
The First Amendment renewed the term of the Facilities and Support Services Agreement for a one year period, beginning on July
1, 2013. The First Amendment also increased the space provided to the Company by Tecogen from approximately 3,071 square feet to
3,282 square feet and from six offices to nine offices. Under the First Amendment, the amount that American DG Energy will pay
the Company for the space and services that it provides under the Facilities and Support Services Agreement increased to $6,495
per month. The First Amendment further clarifies that the total sales thresholds for volume discounts are to be met during a calendar
year and that American DG Energy’s representation rights may be terminated by either the Company or American DG Energy upon
60 days' notice, without cause.

On November 12, 2013, the Company entered
into the Second Amendment to the Facilities, Support Services and Business Agreement, or the Second Amendment. The Second
Amendment modified the exclusivity arrangement of the Facilities and Support Services Agreement between the Company and American
DG Energy to state that in New England States American DG Energy shall have the right to purchase cogeneration products directly
from the Company as described in the agreement so long as American DG Energy intends to retain long-term ownership of the cogeneration
product and utilize it for the production and sale of electricity and thermal energy. The Company will not sell its products to
parties for which the intended use is to earn revenue from metered energy to third parties other than American DG Energy. In cases
where American DG Energy has the opportunity to sell cogeneration products to an unaffiliated party in the New England States and
where the Company has no other appointed representation in that specific region, American DG Energy may buy/resell the cogeneration
product as specified under the terms of the Facilities and Support Services Agreement. If, however, the Company has appointed a
local exclusive representative in that specific New England region, American DG Energy will defer to the local representative for
pricing and other specific details for working cooperatively.

In July 2013, the Company obtained a letter
of credit for approximately $1.1 million in connection with a performance guarantee for certain of its turnkey installations. This
letter of credit was collateralized by $1.055 million in personal funds by John N. Hatsopoulos. If Mr. Hatsopoulos had not provided
this collateral, the Company may have been required to provide the collateral itself, and may not have been able to do so.

On November 12, 2013, the Company entered
into the Second Amendment to the Facilities, Support Services and Business Agreement, or the ADG Amendment, American DG Energy.
The Amendment modifies the exclusivity arrangement of the Facilities, Support Services and Business Agreement between the Company
and American DG Energy.

On November 12, 2013, Ilios entered into
the First Amendment to the Sales Representative Agreement with American DG Energy Inc. The Amendment modifies and defines territories
covered under the Agreement.

The Company subleases portions of its corporate
offices and manufacturing facility to sub-tenants under annual sublease agreements. For the years ended December 31,
2013 and 2012, the Company received $113,784 and $158,898, respectively, from American DG Energy, Levitronix LLC and Alexandros
Partners LLC. In addition, for the years ended December 31, 2013 and 2012 the Company received from the same companies, $90,348
and $101,218, respectively, to offset common operating expenses incurred in the administration and maintenance of its corporate
office and warehouse facility.

Our headquarters is located in Waltham,
Massachusetts, and consists of approximately 43,000 square feet of leased space, of which Tecogen occupies approximately 34,600
square feet of manufacturing, storage and office space. We sub-lease the remaining space to Ilios, American DG Energy, and other
tenants. Our lease, with an original expiration date of March 31, 2014, was renewed for an additional ten years and will expire
March 31, 2024. We believe that our facilities are appropriate and adequate for our current needs.

Revenue from sales of cogeneration and chiller
systems, parts and service to American DG Energy during the years ended December 31, 2013 and 2012 amounted to $758,930 and
$3,795,666, respectively. In addition, Tecogen pays certain operating expenses, including benefits and insurance, on behalf of
American DG Energy. Tecogen was reimbursed for these costs. As of December 31, 2013 the total amount due to American DG Energy
was $119,667. As of December 31, 2012, the total amount due from American DG Energy was $70,811.

74

For additional disclosure related to our
related parties and related party transactions see Note 13 — Related party transactions to our financial statements
included in this prospectus.

Policies and Procedures for Related Person
Transactions

Our Board of Directors will adopt a written
related person transaction policy to set forth the policies and procedures for the review and approval or ratification of related
person transactions. This policy will cover any transaction, arrangement, or relationship, or any series of similar transactions,
arrangements, or relationships, in which we were or are to be a participant where the amount involved exceeds $120,000, and a related
person had or will have a direct or indirect material interest, including, without limitation, purchases of goods or services by
or from the related person or entities in which the related person has a material interest, indebtedness, guarantees of indebtedness,
and employment by us of a related person.

Any related person transaction proposed
to be entered into by us will be required to be reported to our Chief Financial Officer and will be reviewed and approved by the
Audit Committee in accordance with the terms of the policy, prior to effectiveness or consummation of the transaction, whenever
practicable. If our Chief Financial Officer determines that advance approval of a related person transaction is not practicable
under the circumstances, the Audit Committee will review and, in its discretion, may ratify the related person transaction at the
next meeting of the Audit Committee, or at the next meeting following the date that the related person transaction comes to the
attention of our Chief Financial Officer. Our Chief Financial Officer, however, may present a related person transaction arising
in the time period between meetings of the Audit Committee to the chair of the Audit Committee, who will review and may approve
the related person transaction, subject to ratification by the Audit Committee at the next meeting of the Audit Committee.

In addition, any related person transaction
previously approved by the Audit Committee or otherwise already existing that is ongoing in nature will be reviewed by the Audit
Committee annually to ensure that such related person transaction has been conducted in accordance with the previous approval granted
by the Audit Committee, if any, and that all required disclosures regarding the related person transaction are made.

Transactions involving compensation of executive
officers will be reviewed and approved by the Compensation Committee in the manner specified in the charter of the Compensation
Committee.

A related person transaction reviewed under
this policy will be considered approved or ratified if it is authorized by the Audit Committee in accordance with the standards
set forth in our related person transaction policy after full disclosure of the related person’s interests in the transaction.
As appropriate for the circumstances, the Audit Committee will review and consider:

•

the related person’s interest in the related person transaction;

•

the approximate dollar value of the amount involved in the related person transaction;

•

the approximate dollar value of the amount of the related person’s interest in the transaction without regard to the
amount of any profit or loss;

•

whether the transaction was undertaken in the ordinary course of business;

•

whether the transaction with the related person is proposed to be, or was, entered into on terms no less favorable to us than
terms that could have been reached with an unrelated third party;

•

the purpose of, and the potential benefits to us of, the transaction; and

•

any other information regarding the related person transaction or the related person in the context of the proposed transaction
that would be material to stockholders in light of the circumstances of the particular transaction.

The Audit Committee will review all relevant
information available to it about the related person transaction. The Audit Committee may approve or ratify the related person
transaction only if the Audit Committee determines that, under all of the circumstances, the transaction is in, or is not inconsistent
with, our best interests. The Audit Committee may, in its sole discretion, impose conditions as it deems appropriate on us or the
related person in connection with approval of the related person transaction.

75

DESCRIPTION OF COMMON STOCK

General

The following description of our capital
stock and provisions of our amended and restated certificate of incorporation and bylaws are summaries and are qualified by reference
to the charter and the bylaws that will be in effect upon the effectiveness of this registration statement. These documents are
filed as exhibits hereto.

Upon the effectiveness of this registration
statement, our authorized capital stock will consist of 100,000,000 shares of Common Stock, par value $0.001 per share. Information
concerning our outstanding Common Stock and stock options is contained in the section entitled “Outstanding Securities and
Shares Eligible for Future Sale.”

The following description summarizes information
about our capital stock. You can obtain more comprehensive information about our capital stock by reviewing our certificate of
incorporation and bylaws as well as the Delaware General Corporation Law.

Common Stock

Voting Rights. Each holder
of Common Stock is entitled to one vote per share on all matters properly submitted to a vote of the stockholders, including the
election of directors. Our charter will not provide for cumulative voting rights. Because of this, but subject to the rights of
any then outstanding shares of preferred stock, the holders of a majority of the shares of Common Stock entitled to vote in any
election of directors can elect all of the directors standing for election, if they should so choose. An election of directors
by our stockholders is determined by a plurality of the votes cast by stockholders entitled to vote on the election.

Dividends. Subject to
preferences that may be applicable to any then outstanding preferred stock, the holders of our outstanding shares of Common Stock
are entitled to receive dividends, if any, as may be declared from time to time by our Board of Directors out of legally available
funds.

Liquidation. In the event
of our liquidation, dissolution or winding up, holders of Common Stock will be entitled to share ratably in the net assets legally
available for distribution to stockholders after the payment of all of our debts and other liabilities, subject to the satisfaction
of any liquidation preference granted to the holders of any outstanding shares of preferred stock.

Rights and Preferences. Holders
of our common stock have no preemptive, conversion or subscription rights, and there are no redemption or sinking fund provisions
applicable to our common stock.

Delaware Anti-Takeover Law and Charter and Bylaws Provisions

Delaware Anti-Takeover Law. We
are subject to Section 203 of the Delaware General Corporation Law. Section 203 of that law generally prohibits a public Delaware
corporation from engaging in a “business combination” with an “interested stockholder” for a period of
three years after the date of the transaction in which the person became an interested stockholder, unless the interested stockholder
attained such status with the approval of our Board of Directors, the business combination is approved in a prescribed manner or
the interested stockholder acquired at least 85% of our outstanding voting stock in the transaction in which it became an interested
stockholder. A “business combination” includes, among other things, a merger or consolidation involving us and the
“interested stockholder” and the sale of more than 10% of our assets. In general, an “interested stockholder”
is any entity or person beneficially owning 15% or more of our outstanding voting stock and any entity or person affiliated with
or controlling or controlled by such entity or person.

76

Certificate of Incorporation and Bylaws. Provisions
of our certificate of incorporation and bylaws may delay or discourage transactions involving an actual or potential change of
control or change in our management, including transactions in which stockholders might otherwise receive a premium for their shares,
or transactions that our stockholders might otherwise deem to be in their best interests. Therefore, these provisions could adversely
affect the price of our common stock if and when it becomes tradable. Among other things, our charter and bylaws:

•

authorize the issuance of “blank check” preferred stock, the terms of which may be established and shares of which
may be issued without stockholder approval;

•

eliminate the ability of stockholders to call a special meeting of stockholders; and

•

establish advance notice requirements for nominations for election to the Board of Directors or for proposing matters that
can be acted upon at stockholder meetings.

The amendment of any provisions of our charter
by the stockholders would require the approval of the holders at least two-thirds of our then outstanding Common Stock. Our by-laws
may be amended or repealed by a majority vote of our Board of Directors or by the affirmative vote of the holders of at least two-thirds
of our then outstanding Common Stock.

NASDAQ Capital Market

We have applied to list our common stock
on the NASDAQ Capital Market on the effectiveness of this registration statement.

Authorized but Unissued Shares

The authorized but unissued shares of Common
Stock and preferred stock are available for future issuance without stockholder approval, subject to any limitations imposed by
regulatory authorities. These additional shares may be used for a variety of corporate finance transactions, acquisitions and employee
benefit plans. The existence of authorized but unissued and unreserved Common Stock and preferred stock could make it more difficult
or discourage an attempt to obtain control of us by means of a proxy contest, tender offer, merger or otherwise.

Transfer Agent and Registrar

The transfer agent and registrar for our
common stock will be VStock Transfer LLC.

77

OUTSTANDING SECURITIES AND SHARES ELIGIBLE
FOR FUTURE SALE

Immediately prior to this offering, there
has been no public market for our common stock. Future sales of substantial amounts of Common Stock in the public market could
adversely affect prevailing market prices. The Company does not have any lock-up agreements or registration rights agreements requiring
future registration of our common stock.

Outstanding Common Stock

As of March 31, 2014 there were 246 holders
of record of our common stock. See “Principal Stockholders” for information on the holders of our common stock. Also
see “Description of Securities” for a description of our outstanding and issued capital stock.

Stock Options

As of March 31, 2014, we had 1,186,325 options
outstanding under our incentive stock plan at a weighted average exercise price of $2.22. As of such date, 812,313 of those options
were exercisable.

Warrants

As of March 31, 2014, there were no warrants
outstanding.

SEC Rules Governing Resales of our common stock

The shares of our common stock covered by
this prospectus are freely transferable without restriction. In addition, there are two SEC rules that permit the resale of our
common stock held by our affiliates and the resale of Common Stock sold in private placements that are not covered by this prospectus.

Rule 144

In general, pursuant to Rule 144, under
the Securities Act, as currently in effect, a person (or persons whose shares are aggregated) who is not deemed to have been an
affiliate of ours at any time during the three months preceding a sale, and who has beneficially owned restricted securities within
the meaning of Rule 144 for a least six months (including certain periods of consecutive ownership of preceding non-affiliated
holders) would be entitled to sell those shares, subject only to the availability of current public information about us. Under
Rule 144, a person who is not deemed to have been one of our affiliates at any time during the 3 months preceding a sale, and who
has beneficially owned the shares proposed to be sold for at least one year is entitled to sell the shares without restriction.

On the other hand, our affiliates or persons
selling shares on behalf of our affiliates who own shares that were acquired from us or an affiliate of ours at least six months
prior to the proposed sale are entitled to sell within any three-month period beginning 90 days after the date of this prospectus,
a number of shares that does not exceed the greater of:

•

1% of the number of shares of our common stock then outstanding, which will equal approximately 151,566 shares of our common
stock estimated as of the date of this prospectus; or

•

The average weekly trading volume of our common stock during the four calendar weeks preceding the filing of a notice on Form
144 with respect to such sale, or if no such notice is required, the date of receipt of the order to execute the transaction by
a broker or the execution of the transaction directly with a market maker.

Sales under Rule 144 by our affiliates
or persons selling shares on behalf of our affiliates are also subject to certain manner of sale provisions and notice requirements
and to the availability of current public information about us.

78

Rule 701

Rule 701 provides that the shares of Common
Stock acquired upon the exercise of currently outstanding options or other rights granted under our equity plans may be resold
by persons, other than affiliates, restricted only by the manner of sale provisions of Rule 144, and by affiliates in accordance
with Rule 144 without compliance with its one-year minimum holding period.

Shares Eligible for Future Sale

Based on the number of shares of Common
Stock outstanding as of March 31, 2014, upon the closing of this offering:

•

The shares sold in this offering will be available for sale without restriction;

•

The 2,028,145 shares registered in a secondary offering will be available for sale without restriction;

•

5,725,034 shares will be held by non-affiliates for more than six months and will be available for sale without restriction;

•

5,600 shares will be held by non-affiliates for less than six months and will become available for sale without restriction
once they are held for six months; and

•

7,849,440 shares will be held by affiliates, of which 25,000 shares will be held by affiliates for less than six months and
will become available for sale under Rule 144 once they are held for six months, and 7,824,440 shares are available for sale under
Rule 144 or Rule 701, as described above.

On February 6, 2014, in order to satisfy
our contractual obligations to certain investors in a private placement, we filed a registration statement on Form S-1 with the
SEC seeking to register 2,028,145 shares of our common stock for resale or other disposition by the selling stockholders named
therein. Once the registration statement for the secondary offering has been declared effective by the SEC, the shares offered
thereby will be available for sale without restriction. None of the selling stockholders in the secondary offering will be subject
to lock-up agreements in connection with this offering.

Lock-up Agreements

Our officers, directors, employees, option
holders and stockholders owning more than 5% of our outstanding common stock have agreed, subject to certain exceptions, for a
period of 180 days after the date of this prospectus, not to offer, sell, contract to sell, pledge, grant any option to purchase,
make any short sale or otherwise dispose of, directly or indirectly any shares of our common stock or any securities convertible
into or exchangeable for shares of our common stock either owned as of the date hereof or thereafter acquired without the prior
written consent of the Placement Agent. The Placement Agent may, in its sole discretion and at any time or from time to time before
the termination of the lock-up period, without notice, release all or any portion of the securities subject to lock-up agreements.

79

PLAN OF DISTRIBUTION

Scarsdale Equities LLC, which we refer
to as the Placement Agent, has agreed to act as the exclusive placement agent in connection with this offering subject to the
terms and conditions of a placement agent agreement, dated .
The Placement Agent may engage selected dealers to assist in the placement of the shares. The Placement Agent is not purchasing
or selling any shares offered by this prospectus, nor is it required to arrange the purchase or sale of any specific number or
dollar amount of the shares, but has agreed to use its commercially reasonable efforts to arrange for the sale of all of the shares
offered hereby. We will enter into subscription agreements directly with investors in connection with this offering and we may
not sell the entire amount of shares offered pursuant to this prospectus. The price per share has been determined based upon arm’s-length
negotiations between the investors and us.

The Placement Agent proposes to arrange
for the sale to one or more investors of the shares offered pursuant to this prospectus through direct subscription agreements
between the investors and us.

Commissions and Expenses

We have agreed to pay the Placement Agent
an aggregate cash placement fee equal to 6.75% of the gross proceeds in this offering.

The following table shows the per share
and total cash Placement Agent’s fees we will pay to the Placement Agent in connection with the sale of the shares offered
pursuant to this prospectus assuming the purchase of all of the shares offered hereby:

Per Share

$

Total

$

Because there is no minimum offering amount
required as a condition to closing in this offering, the actual total offering commissions, if any, are not presently determinable
and may be substantially less than the maximum amount set forth above. We have also agreed to reimburse the Placement Agent for
its reasonable out-of-pocket expenses in connection with the offering, including the reasonable legal fees and disbursements of
its counsel subject to a cap of $50,000 for such legal fees and disbursements. We have placed $35,000 in an escrow account to partially
secure our expense reimbursement obligation.

Our obligation to issue and sell shares
to the investors is subject to the conditions set forth in the subscription agreements, which may be waived by us at our discretion.
An investor’s obligation to purchase shares is subject to the conditions set forth in his or her subscription agreement as
well, which may also be waived.

We currently anticipate that the sale of
the shares will be completed on or about , 2014. We estimate the total offering expenses
of this offering that will be payable by us, excluding placement agent fees, will be approximately $450,000, which includes legal
and printing costs, various other fees and reimbursement of the Placement Agent’s expenses. At the closing, The Depository
Trust Company will credit the shares of common stock to the respective accounts of the investors.

No Public Market

Prior to this offering, there has not been
a public market for our common stock, and the public offering price for our common stock will be determined through negotiations
between us and the investors in the offering. Among the factors to be considered in these negotiations will be:

•

our status of business development;

•

our new business structure and operations;

•

prevailing market conditions, including the history and prospects for our industry;

•

market valuations of other companies that we and the Placement Agent believe to be comparable to us;

80

•

our future prospects and the experience of our management;

•

our capital structure; and

•

other factors deemed relevant.

No assurance can be given that the public
offering price will correspond to the price at which our common stock will trade in the public market subsequent to this offering
or that an active trading market for our common stock will develop and continue after this offering. See “Determination of
Offering Price” in this prospectus for more information regarding the determination of the public offering price.

Indemnification

We have agreed to indemnify the Placement
Agent against liabilities under the Securities Act. We have also agreed to contribute to payments the Placement Agent may be required
to make in respect of such liabilities.

NASDAQ Listing

We have applied to list our common stock
on the NASDAQ Capital Market under the symbol “TGEN”.

Lock-up Agreements

We, our officers, directors, employees,
option holders and stockholders owning more than 5% of our outstanding common stock have agreed, subject to certain exceptions,
for a period of 180 days after the date of this prospectus, not to offer, sell, contract to sell, pledge, grant any option to purchase,
make any short sale or otherwise dispose of, directly or indirectly any shares of our common stock or any securities convertible
into or exchangeable for shares of our common stock either owned as of the date hereof or thereafter acquired without the prior
written consent of the Placement agent. This 180-day period may be extended if (1) during the last 17 days of the 180-day period,
we issue an earnings release or material news or a material event regarding us occurs or (2) prior to the expiration of the 180-day
period, we announce that we will release earnings results during the 16-day period beginning on the last day of the 30-day period,
then the period of such extension will be 18-days, beginning on the issuance of the earnings release or the occurrence of the material
news or material event. If after any announcement described in clause (2) of the preceding sentence, we announce that we will not
release earnings results during the 16-day period, the lock-up period shall expire the later of the expiration of the 180-day period
and the end of any extension of such period made pursuant to clause (1) of the preceding sentence. The Placement Agent may, in
its sole discretion and at any time or from time to time before the termination of the lock-up period, without notice, release
all or any portion of the securities subject to lock-up agreements.

Electronic Distribution

This prospectus may be made available in
electronic format on websites or through other online services maintained by the Placement Agent, or by an affiliate of the Placement
Agent. Other than this prospectus in electronic format, the information on the Placement Agent’s website and any information
contained in any other website maintained by the Placement Agent is not part of this prospectus or the registration statement of
which this prospectus forms a part, has not been approved and/or endorsed by us or the Placement Agent, and should not be relied
upon by investors.

The foregoing does not purport to be a
complete statement of the terms and conditions of the placement agent agreement and subscription agreements. A copy of the placement
agent agreement and the form of subscription agreement with the investors are included as exhibits to the registration statement
of which this prospectus is a part. See “Where You Can Find Additional Information” on page 84.

81

Regulation M Restrictions

The Placement Agent may be deemed to be
an underwriter within the meaning of Section 2(a)(11) of the Securities Act, and any commissions received by it and any profit
realized on the resale of the shares sold by it while acting as a principal might be deemed to be an underwriting discount or commission
under the Securities Act. As an underwriter, the Placement Agent would be required to comply with the requirements of the Securities
Act and the Exchange Act, including, without limitation, Rule 415(a)(4) under the Securities Act and Rule 10b-5 and Regulation
M under the Exchange Act. These rules and regulations may limit the timing of purchases and sales of shares by the Placement Agent
acting as principal. Under these rules and regulations, the placement agent may not:

•

engage in any stabilization activity in connection with our securities; and

•

bid for or purchase any of our securities or attempt to induce any person to purchase any of our securities, other than as
permitted under the Exchange Act, until it has completed its participation in the distribution.

Other

Ardour Capital Investments, LLC, which
we refer to as the Selected Dealer, entered into a Selected Dealers Agreement with the Placement Agent in connection with this
offering. From time to time, the Placement Agent, the Selected Deal and their respective affiliates have provided, and may
in the future provide, various investment banking, financial advisory and other services to us and our affiliates for which services
they have received, and may in the future receive, customary fees. In the course of their businesses, the Placement Agent, the
Selected Dealer and their respective affiliates may actively trade our securities or loans for their own account or for the accounts
of customers, and, accordingly, the Placement Agent, the Selected Dealer and their respective affiliates may at any time hold
long or short positions in such securities or loans. Except for services provided in connection with this offering, and except
as described below, the Placement Agent, the Selected Dealer and their respective affiliates have not provided any investment
banking or other financial services to us during the 180-day period preceding the date of this prospectus and we do not expect
to retain any placement agent to perform any investment banking or other financial services for us for at least 90 days after
the date of this prospectus. In November 2013, the Placement Agent acted as our placement agent in connection with certain private
placements of our securities for which we paid the Placement Agent $276,553 in commissions. In December 2013, the Selected
Dealer acted as our placement agent in connection with certain private placements of our securities for which we paid the Selected
Dealer $255,000 in commissions.

Certain Relationships

Francis A. Mlynarczyk, Jr., the Registered
Principal and Managing Member of the Placement Agent, is also a director of American DG Energy, one of our affiliated entities.
In addition, Mr. Mlynarczyk through an investment account, IRA FBO Francis A. Mlynarczyk, Jr. Pershing LLC as Custodian, beneficially
owns 5,600 shares of our common stock.

EXPERTS

The consolidated financial statements as
of December 31, 2013 and 2012 and for the years then ended, appearing in this registration statement and prospectus have been
audited by McGladrey LLP, an independent registered public accounting firm, as stated in their report appearing elsewhere herein,
and are included in reliance upon such report and upon the authority of such firm as experts in accounting and auditing.

No expert or counsel named in this prospectus
as having prepared or certified any part of this prospectus or having given an opinion upon the validity of the securities being
registered or upon other legal matters in connection with the registration or offering of the Common Stock was employed on a contingency
basis, or had, or is to receive, any interest, directly or indirectly, in our Company or any of our parents or subsidiaries. Nor
was any such person connected with us or any of our parents or subsidiaries, if any, as a promoter, managing or principal underwriter,
voting trustee, director, officer, or employee.

82

LEGAL MATTERS

The validity of our common stock offered
under this prospectus will be passed upon by Sullivan & Worcester LLP, Boston, Massachusetts. Lowenstein Sandler LLP, New York,
New York, is acting as counsel to the Placement Agent in connection with this offering.

WHERE YOU CAN FIND ADDITIONAL INFORMATION

We have filed with the SEC a registration
statement on Form S-1, including exhibits and schedules, under the Securities Act with respect to the shares of common stock to
be sold in this offering. This prospectus, which constitutes a part of the registration statement, does not contain all of the
information set forth in the registration statement or the exhibits and schedules that are part of the registration statement.
For further information about us and our securities, you should refer to the registration statement.

We are subject to the information and reporting
requirements of the Exchange Act and are required to file annual, quarterly, and current reports, proxy statements, and other information
with the SEC. You may read, without charge, and copy, at prescribed rates, all or any portion of the registration statement or
any reports, statements, or other information in the files at the public reference room at the SEC’s principal office at
100 F Street NE, Washington, D.C., 20549, Room 1580. You may request copies of these documents, for a copying fee, by writing to
the SEC. You may call the SEC at 1-800-SEC-0330 for further information on the operation of its public reference room. Our filings,
including the registration statement, are also available to you on the Internet website maintained by the SEC at http://www.sec.gov.

83

INDEX TO CONSOLIDATED FINANCIAL STATEMENTS

The Financial Statements included below
are stated in U.S. dollars and are prepared in accordance with U.S. Generally Accepted Accounting Principles. The following table
summarizes the relevant financial data for our business and should be read with our financial statements, which are included in
this registration statement.

Audited Financial Statements

Report of Independent Registered Public Accounting Firm McGladrey LLP

F-2

Consolidated Balance Sheets as of December 31, 2013 and 2012

F-3

Consolidated Statements of Operations for the years ended December 31, 2013 and 2012

F-4

Consolidated Statements of Changes in Stockholders’ Equity for the years ended December 31, 2013 and 2012

F-5

Consolidated Statements of Cash Flows for the years ended December 31, 2013 and 2012

F-6

Notes to Audited Consolidated Financial Statements

F-8

All other schedules for which provision
is made in the applicable accounting regulations of the SEC are not required under the related instructions, or are inapplicable,
and therefore have been omitted.

F-1

Report of Independent Registered Public Accounting Firm

To the Board of Directors and Stockholders of

Tecogen Inc.

We have audited the accompanying consolidated
balance sheets of Tecogen Inc. as of December 31, 2013 and 2012, and the related consolidated statements of operations, stockholders'
equity, and cash flows for the years then ended. These financial statements are the responsibility of the Company's management.
Our responsibility is to express an opinion on these financial statements based on our audits.

We conducted our audits in accordance with
the standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform
the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement. The Company
is not required to have, nor were we engaged to perform, an audit of its internal control over financial reporting. Our audits
included consideration of internal control over financial reporting as a basis for designing audit procedures that are appropriate
in the circumstances, but not for the purpose of expressing an opinion on the effectiveness of the Company’s internal control
over financial reporting. Accordingly, we express no such opinion. An audit also includes examining, on a test basis, evidence
supporting the amounts and disclosures in the financial statements, assessing the accounting principles used and significant estimates
made by management, as well as evaluating the overall financial statement presentation. We believe that our audits provide a reasonable
basis for our opinion.

In our opinion, the consolidated financial
statements referred to above present fairly, in all material respects, the financial position of Tecogen Inc. as of December 31,
2013 and 2012, and the results of its operations and its cash flows for the years then ended, in conformity with U.S. generally
accepted accounting principles.

Proceeds from issuance of demand notes payable and line of credit, related party

1,650,000

300,000

Proceeds from sale of common stock, net of costs

5,966,805

680,000

Proceeds from exercise of stock options

3,000

—

Proceeds from issuance of senior convertible promissory note

3,000,000

—

Payments from debt issuance costs

(140,433

)

—

Purchase of restricted stock

(350

)

(337

)

Proceeds from sale of subsidiary common stock

—

500,000

Net cash provided by financing activities

10,441,522

1,584,663

Net increase (decrease) in cash and cash equivalents

6,141,114

(1,445,781

)

Cash and cash equivalents, beginning of the year

1,572,785

3,018,566

Cash and cash equivalents, end of the year

$

7,713,899

$

1,572,785

Supplemental disclosures of cash flows information:

Cash paid for interest

$

55,639

$

—

Non-cash investing and financing activities:

Conversion of accrued convertible debenture interest into common stock

$

11,280

$

6,100

Conversion of related party notes to common stock

$

90,967

$

100,000

Settlement of shareholder receivable

$

—

$

240,000

The accompanying notes are an integral part
of these consolidated financial statements.

F-6

Notes to Audited Consolidated Financial Statements

Note 1 – Nature of business and operations

Tecogen Inc. (the “Company”)
(a Delaware Corporation) was organized on November 15, 2000, and acquired the assets and liabilities of the Tecogen Products division
of Thermo Power Corporation. The Company produces commercial and industrial, natural-gas-fueled engine-driven, combined heat and
power (CHP) products that reduce energy costs, decrease greenhouse gas emissions and alleviate congestion on the national power
grid. Tecogen’s products supply electric power or mechanical power for cooling, while heat from the engine is recovered and
purposefully used at a facility. The majority of Company’s customers are located in regions with the highest utility rates,
typically California, the Midwest and the Northeast.

On May 4, 2009 the Company invested
$8,400 in exchange for 8,400,000 shares of a newly established corporation Ilios Inc., or Ilios. The investment gave the Company
a controlling financial interest in Ilios, whose business focus is advanced heating systems for commercial and industrial applications.
On May 11, 2009 the Company sold 1,400,000 shares in Ilios at $0.50 per share to two of its existing stockholders in exchange for
the extinguishment of $700,000 in demand notes payable, convertible debentures and accrued interest (see Note 7 – Demand
notes payable and convertible debentures – related party). On July 24, 2009, Ilios sold 2,710,000 shares of common
stock to accredited investors at $0.50 per share and raised $1,352,500. On June 3, 2011, Ilios sold 500,000 shares of common stock
to Tecogen at $0.50 per share and raised $250,000 and on December 29, 2011, Ilios sold 1,000,000 shares of common stock to Tecogen
at $0.50 per share and raised $500,000. On January 19, 2012, Ilios sold 1,000,000 shares of common stock to an accredited investor
and raised $500,000. On December 28, 2012, Ilios sold 1,000,000 shares of common stock to Tecogen at $0.50 per share and raised
$500,000. As of December 31, 2013 the Company owns a 65.0% interest in Ilios and has consolidated Ilios into its financial
statements.

The accompanying consolidated financial
statements include the accounts of the Company and its majority owned subsidiary Ilios, whose business focus is on advanced heating
systems for commercial and industrial applications. With the inclusion of unvested restricted stock awards, the Company owns 63.7%
of Ilios.

The Company’s operations are comprised
of one business segment. Our business is to manufacture and support highly efficient CHP products based on engines fueled by natural
gas.

Note 2 – Summary of significant accounting policies

Principles of Consolidation and Basis of Presentation

The financial statements have been prepared
in accordance with accounting standards set by the Financial Accounting Standards Board (FASB). The FASB sets generally accepted
accounting principles (GAAP) to ensure financial condition, results of operations, and cash flows are consistently reported. References
to GAAP issued by the FASB in these footnotes are to the FASB Accounting Standards Codification (ASC). The Company adopted the
presentation requirements for noncontrolling interests required by ASC 810 Consolidation. Under ASC 810, earnings or losses
attributed to the noncontrolling interests are reported as part of the consolidated earnings and not a separate component of income
or expense. Noncontrolling interests in the net assets and operations of Ilios are reflected in the caption “Noncontrolling
interest” in the accompanying consolidated financial statements. All intercompany transactions have been eliminated.

Use of Estimates

The preparation of financial statements
in conformity with accounting principles generally accepted in the United States of America requires management to make estimates
and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities
at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results
could differ from those estimates.

F-7

Concentration of Credit Risk

The Company’s financial instruments
that are exposed to concentrations of credit risk consist primarily of cash and cash equivalents, short-term investments and accounts
receivable. The Company maintains its cash balances in bank accounts, which at times may exceed the Federal Deposit Insurance Corporation’s
(“FDIC”) general deposit insurance limits. The amount on deposit at December 31, 2013 and 2012 which exceeded
the $250,000 federally insured limit was approximately $7,410,000 and $1,070,000, respectively. The Company has not experienced
any losses in such accounts and thus believes that it is not exposed to any significant credit risk on cash and cash equivalents.

There was one customer who represented more
than 10% of revenues for the year ended December 31, 2012. The Company has no customers who represented 10% of revenues for
the year ended December 31, 2013. Included in trade accounts receivable are amounts from one customer who represents 22% of
the accounts receivable balance as of December 31, 2013 and another customer who represented 16% of the accounts receivable
balance as of December 31, 2012.

Cash and Cash Equivalents

The Company considers all highly liquid
instruments with an original maturity date, at date of purchase, of three months or less to be cash and cash equivalents.

Short-Term Investments

Short-term investments consist of certificates
of deposit with maturities of greater than three months but less than one year. Certificates of deposits approximate fair value,
based on estimates using current market rates offered for deposits with similar remaining maturities.

On October 26, 2011, the Company entered
into an agreement with Digital Energy Corp., a customer of the Company, whereby the Company provided a letter of credit in the
amount of $180,000, for the benefit of Digital Energy Corp., to satisfy a requirement of the New York Independent System Operator,
Inc. A certificate of deposit for $180,000 secures the letter of credit. In exchange for providing this letter of credit, Digital
Energy Corp. provided a promissory note to the Company for $180,000, with interest at 6%, payable in monthly installments of interest
only. Principal would only be owed if the letter of credit was drawn upon and would become due and payable on the first anniversary
date of the note. On February 19, 2013, this letter of credit was cancelled and the certificate of deposit was released from restriction
and sold.

On June 13, 2011, the Southern California
Gas Company entered into an agreement with the Company to invest $500,000 in the Company’s Common Stock. The agreement
included certain stockholder rights and a redemption right whereby the investor may redeem the shares for cash until the earlier
of, the initiation of a public offering of the Company by filing a registration statement with the SEC, or 5 years. A letter of
credit, secured by a Certificate of Deposit, for the amount of the investment had been put in place to satisfy the contingency
of the redemption right. Since the Company filed a registration statement with the Securities and Exchange Commission on December
23, 2011 the redemption right was no longer valid. The Certificate of Deposit was converted to cash in 2012.

Accounts Receivable

Accounts receivable are stated at the amount
management expects to collect from outstanding balances. An allowance for doubtful accounts is provided for those accounts receivable
considered to be uncollectible based upon historical experience and management’s evaluation of outstanding accounts receivable
at the end of the year. Bad debts are written off against the allowance when identified. At December 31, 2013 and 2012 the
allowance for doubtful accounts was $103,800 and $154,400, respectively.

F-8

Inventory

Raw materials, work in process, and finished
goods inventories are stated at the lower of cost, as determined by the average cost method, or market. The Company periodically
reviews inventory quantities on hand for excess and/or obsolete inventory based primarily on historical usage, as well as based
on estimated forecast of product demand. Any reserves that result from this review are charged to cost of sales.

Property, Plant and Equipment

Property, plant and equipment are recorded
at cost. Depreciation is provided using the straight-line method over the estimated useful lives of the asset, which range from
three to fifteen years. Leasehold improvements are amortized using the straight-line method over the lesser of the estimated useful
lives of the assets or the term of the related leases. Expenditures for maintenance and repairs are expensed currently, while renewals
and betterments that materially extend the life of an asset are capitalized.

Intangible Assets

Intangible assets subject to amortization
include costs incurred by the Company to acquire product certifications, certain patent costs and developed technologies. These
costs are amortized on a straight-line basis over the estimated economic life of the intangible asset. The Company reviews intangible
assets for impairment when the circumstances warrant.

Goodwill

The Company's goodwill was recorded as a
result of the Company's asset acquisition discussed in Note 15. The Company has recorded this transaction using the acquisition
method of accounting. The Company tests its recorded goodwill for impairment as of the last day of the year, or more often if indicators
of potential impairment exist, by determining if the carrying value of the Company's single reporting unit exceeds its estimated
fair value. Factors that could trigger an interim impairment test include, but are not limited to, underperformance relative to
historical or projected future operating results, significant changes in the manner of use of the acquired assets or the Company's
overall business, significant negative industry or economic trends and a sustained period where market capitalization, plus an
appropriate control premium, is less than stockholders' equity.

The Company's impairment test involves a
two-step process. In the first step, the Company compares the fair value of the reporting unit to its carrying value. If the fair
value of the reporting unit exceeds its carrying value, goodwill is not impaired and no further testing is required. If the fair
value of the reporting unit is less than the carrying value, the Company must perform the second step of the impairment test to
measure the amount of impairment loss, if any. In the second step, the reporting unit's fair value is allocated to all of the assets
and liabilities of the reporting unit, including any unrecognized intangible assets, in a hypothetical analysis that calculates
the implied fair value of goodwill in the same manner as if the reporting unit was being acquired in a business combination. If
the implied fair value of the reporting unit's goodwill is less than the carrying value, the difference is recorded as an impairment
loss. As of December 31, 2013, the Company determined that the fair value of the reporting unit exceeded its carrying value
and therefore the second step was not necessary and no impairment was recognized.

Common Stock

The Company's common
stock was split one-for-four in a reverse stock split effective July 22, 2013. The effect of this reverse stock split has been
retroactively applied to per share data and common stock information.

F-9

Impairment of long-lived assets

Long-lived assets, including intangible
assets and property and equipment, are evaluated for impairment whenever events or changes in circumstances have indicated that
an asset may not be recoverable and are grouped with other assets to the lowest level for which identifiable cash flows are largely
independent of the cash flows of other groups of assets and liabilities. If the sum of the projected undiscounted cash flows (excluding
interest charges) is less than the carrying value of the assets, the assets will be written down to the estimated fair value and
such loss is recognized in income from continuing operations in the period in which the determination is made. Management determined
that no impairment of long-lived assets existed as of December 31, 2013.

Off Balance Sheet Arrangements

On July 22, 2013, the Company’s Chief
Executive Officer personally pledged to support a bank credit facility of $1,055,000 to support bank guarantees issued on certain
construction contracts.

Loss per Common Share

The Company computes basic loss per share
by dividing net loss for the period by the weighted-average number of shares of Common Stock outstanding during the period. The
Company computes its diluted earnings per common share using the treasury stock method. For purposes of calculating diluted earnings
per share, the Company considers its shares issuable in connection with the convertible debentures, stock options and warrants
to be dilutive Common Stock equivalents when the exercise/conversion price is less than the average market price of our common
stock for the period. All shares issuable for the years ended December 31, 2013 and 2012 were anti-dilutive because of the
reported net loss.

Other Comprehensive Net Loss

The comprehensive net loss for the years
ended December 31, 2013 and 2012 does not differ from the reported loss.

Segment Information

The Company reports segment data based on
the management approach. The management approach designates the internal reporting that is used by management for making operating
and investment decisions and evaluating performance as the source of the Company's reportable segments. The Company uses one measurement
of profitability and does not disaggregate its business for internal reporting. The Company has determined that it operates in
one business segment which manufactures and supports highly efficient CHP products based on engines fueled by natural gas. All
of the Company’s long lived assets reside in the United States of America. All of the Company’s revenue is generated
in the United States of America.

The following table summarizes net revenue
by product line and services for the years ended December 31, 2013 and 2012:

2013

2012

Products:

Cogeneration

$

5,199,649

$

5,791,412

Chiller

1,146,401

1,661,810

Total Product Revenue

6,346,050

7,453,222

Services

Service contracts

7,071,388

7,089,491

Installations

2,432,431

711,259

Total Service Revenue

9,503,819

7,800,750

$

15,849,869

$

15,253,972

F-10

Income Taxes

The Company uses the asset and liability
method of accounting for income taxes. The current or deferred tax consequences of transactions are measured by applying the provisions
of enacted tax laws to determine the amount of taxes payable currently or in future years. Deferred tax assets and liabilities
are determined based on the difference between the financial statement and tax bases of assets and liabilities and expected future
tax consequences of events that have been included in the financial statements or tax returns using enacted tax rates in effect
for the years in which the differences are expected to reverse. Under this method, a valuation allowance is used to offset deferred
taxes if, based upon the available evidence, it is more likely than not that some or all of the deferred tax assets may not be
realized. Management evaluates the recoverability of deferred taxes and the adequacy of the valuation allowance annually.

The Company has adopted the provisions of
the accounting standards relative to accounting for uncertainties in tax positions. These provisions provide guidance on the recognition,
de-recognition and measurement of potential tax benefits associated with tax positions. The Company elected to recognize interest
and penalties related to income tax matters as a component of income tax expense in the statements of operations. There was no
impact on the financial statements as a result of this guidance.

With few exceptions, the Company is no longer
subject to possible income tax examinations by federal, state or local taxing authorities for tax years before 2009, with the exception
of loss carryforwards in the event they are utilized in future years. The Company's tax returns are open to adjustment from 2001
forward, as a result of the fact that the Company has loss carryforwards from those years, which may be adjusted in the year those
losses are utilized.

Fair Value of Financial Instruments

The Company’s financial instruments
are cash and cash equivalents, certificates of deposit, accounts receivable, accounts payable, demand notes, line of credit and
convertible debentures due to related parties. The recorded values of cash and cash equivalents, accounts receivable and accounts
payable approximate their fair values based on their short-term nature. At December 31, 2013, the recorded value on the consolidated
balance sheet of the debentures approximates fair value as the terms approximate those available for similar instruments. Certificates
of deposits are classified as short-term investments and approximate fair value, based on estimates using current market rates
offered for deposits with similar remaining maturities.

Revenue Recognition

Revenue is recognized when persuasive evidence
of an arrangement exists, delivery has occurred or services have been rendered, the price is fixed or determinable and collectability
is reasonably assured. Generally, sales of cogeneration and chiller units and parts are recognized when shipped and services are
recognized over the term of the service period. Payments received in advance of services being performed are recorded as deferred
revenue.

Infrequently, the Company recognizes revenue
in certain circumstances before delivery has occurred (commonly referred to as bill and hold transactions). In such circumstances,
among other things, risk of ownership has passed to the buyer, the buyer has made a written fixed commitment to purchase the finished
goods, the buyer has requested the finished goods be held for future delivery as scheduled and designated by them, and no additional
performance obligations exist by the Company. For these transactions, the finished goods are segregated from inventory
and normal billing and credit terms granted. For the years ended December 31, 2013 and 2012 no revenues were recorded
as bill and hold transactions.

For those arrangements that include multiple
deliverables, the Company first determines whether each service or deliverable meets the separation criteria of FASB ASC 605-25,
Revenue Recognition—Multiple-Element Arrangements. In general, a deliverable (or a group of deliverables) meets the
separation criteria if the deliverable has stand-alone value to the customer and, if the arrangement includes a general right of
return, delivery or performance of the undelivered item(s) is considered probable and substantially in control of the Company.
Each deliverable that meets the separation criteria is considered a separate ‘‘unit of accounting”. The Company
allocates the total arrangement consideration to each unit of accounting using the relative selling price method. The amount of
arrangement consideration that is allocated to a delivered unit of accounting is limited to the amount that is not contingent upon
the delivery of another unit of accounting.

F-11

When vendor-specific objective evidence
or third-party evidence is not available, adopting the relative fair value method of allocation permits the Company to recognize
revenue on specific elements as completed based on the estimated selling price. The Company generally uses internal pricing
lists that determine sales prices to external customers in determining its best estimate of the selling price of the various deliverables
in multiple-element arrangements. Changes in judgments made in estimating the selling price of the various deliverables could significantly
affect the timing or amount of revenue recognition. The Company enters into sales arrangements with customers to sell its
cogeneration and chiller units and related service contracts and occasionally installation services. Based on the fact that
the Company sells each deliverable to other customers on a stand-alone basis, the company has determined that each deliverable
has a stand-alone value. Additionally, there are no rights of return relative to the delivered items; therefore, each deliverable
is considered a separate unit of accounting.

After the arrangement consideration has
been allocated to each unit of accounting, the Company applies the appropriate revenue recognition method for each unit of accounting
based on the nature of the arrangement and the services included in each unit of accounting. Cogeneration and chiller units
are recognized when shipped and services are recognized over the term of the applicable agreement, or as provided when on a time
and materials basis.

In some cases, our customers may choose
to have the Company engineer and install the system for them rather than simply purchase the cogeneration and/or chiller units.
In this case, the Company accounts for revenue, or turnkey revenue, and costs using the percentage-of-completion method of accounting.
Under the percentage-of-completion method of accounting, revenues are recognized by applying percentages of completion to the total
estimated revenues for the respective contracts. Costs are recognized as incurred. The percentages of completion are determined
by relating the actual cost of work performed to date to the current estimated total cost at completion of the respective contracts.
When the estimate on a contract indicates a loss, the Company’s policy is to record the entire expected loss, as required
by generally accepted accounting principles. The excess of contract costs and profit recognized to date on the percentage-of-completion
accounting method in excess of billings is recorded as unbilled revenue. Billings in excess of related costs and estimated earnings
are recorded as deferred revenue.

Presentation of Sales Taxes

The Company reports revenues net of any
revenue-based taxes assessed by governmental authorities that are imposed on and concurrent with specific revenue-producing transactions.

Shipping and Handling Costs

The Company classifies freight billed to
customers as sales revenue and the related freight costs as cost of sales.

Advertising Costs

The Company expenses the costs of advertising
as incurred. For the years ended December 31, 2013 and 2012, advertising expense was approximately $242,200 and $187,500,
respectively.

Research and Development Costs

Internal research and development expenditures
are expensed as incurred. Proceeds from certain grants and contracts with governmental agencies and their contractors to conduct
research and development for new CHP technologies or to improve or enhance existing technology is recorded as an offset to the
related research and development expenses. These grants and contracts are paid on a cost reimbursement basis provided in the agreed
upon budget. Amounts received totaled $127,500 and $126,500 in fiscal years 2013 and 2012, respectively, which offset the Company’s
total research and development expenditures of approximately $867,000 and $431,000 for each of the years ended December 31,
2013 and 2012, respectively, which are included in general and administrative expenses in the accompanying consolidated statements
of operations.

F-12

Stock-Based Compensation

Stock-based compensation cost is measured
at the grant date, based on the estimated fair value of the award, and is recognized as an expense in the statements of operations
over the requisite service period.

The determination of the fair value of share-based
payment awards is affected by the Company’s stock price. Since the Company was not publicly traded when the awards were issued,
the Company considered the sales price of the Common Stock in private placements to unrelated third parties as a measure of the
fair value of its Common Stock.

The Company utilizes an estimated forfeiture
rate when calculating the expense for the period. Forfeitures are estimated at the time of grant and revised, if necessary, in
subsequent periods if actual forfeitures differ from those estimates. Stock-based compensation expense recognized is based on awards
that are ultimately expected to vest. The Company evaluates the assumptions used to value awards regularly and if factors change
and different assumptions are employed, stock-based compensation expense may differ significantly from what has been recorded in
the past. If there are any modifications or cancellations of the underlying unvested securities, the Company may be required to
accelerate, increase or cancel any remaining unearned stock-based compensation expense.

Pursuant to ASC 505-50, Equity Based
Payments to Non-Employees, the fair value of restricted Common Stock and stock options issued to nonemployees is revalued at
each reporting period until the ultimate measurement date, as defined by ASC 505-50. The Company records the value of the instruments
at the time services are provided and the instruments vest. Accordingly, the ultimate expense is not fixed until such instruments
are fully vested.

Reclassifications

Certain prior period balances have been
reclassified to conform with current period presentation. As a result of a four-for-one reverse stock split which took place during
the year, a reclassification of $40,836 from common stock to additional paid in capital was retroactively applied to the balances
as of December 31, 2012. Also, installation revenue is broken out in the schedule of net revenue by product line and services above;
in the prior year this revenue was included in services.

Note 3 – Loss per common share:

Basic and diluted earnings per share for
the years ended December 31, 2013 and 2012, respectively, were as follows:

2013

2012

Loss available to stockholders

$

(3,449,489

)

$

(1,636,957

)

Weighted average shares outstanding - Basic and diluted

13,385,155

13,135,071

Basic and diluted loss per share

$

(0.26

)

$

(0.12

)

Anti-dilutive shares underlying stock options outstanding

1,148,000

1,096,500

Anti-dilutive convertible debentures

555,556

75,806

F-13

Note 4 – Inventory

Inventories at December 31,
2013 and 2012 consisted of the following.

2013

2012

Gross raw materials

$

3,539,732

$

3,574,620

Less - reserves

(300,000

)

(332,000

)

Net raw materials

3,239,732

3,242,620

Work-in-process

104,061

114,002

Finished goods

—

—

$

3,343,793

$

3,356,622

Note 5 – Intangible assets other
than goodwill

The Company capitalized $171,224 and $17,314
of product certification costs during the years ended December 31, 2013 and 2012, respectively. Also included in intangible
assets are the costs incurred by the Company to acquire certain patents. These patents, once in service, will be amortized on a
straight-line basis over the estimated economic life of the associated product, which range from approximately 7-10 years. The
Company capitalized $226,726 and $146,981 of patent-related costs during the years ended December 31, 2013 and 2012, respectively.
The Company also capitalized $240,000 certain developed technology in connection with an asset acquisition which is being amortized
over its useful life of fifteen years. Intangible assets at December 31, 2013 and 2012 consist of the following:

Product Certifications

Patents

Developed Technology

Total

Balance at December 31, 2013

Intangible assets

$

406,706

$

441,609

240,000

$

1,088,315

Less - accumulated amortization

(83,405

)

(39,583

)

(12,000

)

(134,988

)

$

323,301

$

402,026

$

228,000

$

953,327

Balance at December 31, 2012

Intangible assets

$

235,482

$

214,883

—

$

450,365

Less - accumulated amortization

(57,798

)

(20,547

)

—

(78,345

)

$

177,684

$

194,336

$

—

$

372,020

Amortization expense was $56,643 and $33,896
during the years ended December 31, 2013 and 2012, respectively. Estimated amortization expense at December 31, 2013
for each of the five succeeding years is as follows:

2014

$

80,937

2015

119,758

2016

119,758

2017

119,758

2018

113,560

Thereafter

399,556

$

953,327

F-14

Note 6 – Property and equipment

Property and equipment at December 31,
2013 and 2012 consisted of the following:

Estimated Useful Life (in Years)

2013

2012

Machinery and equipment

5 - 7 years

$

773,894

$

478,290

Furniture and fixtures

5 years

79,612

54,058

Computer software

3 - 5 years

67,215

56,935

Leasehold improvements

*

397,158

326,366

1,317,879

915,649

Less - accumulated depreciation and amortization

(679,853

)

(480,037

)

Net property, plant and equipment

$

638,026

$

435,612

* Lesser
of estimated useful life of asset or lease term

Depreciation and amortization expense on
property and equipment for the years ended December 31, 2013 and 2012 was $199,816 and $169,879, respectively. Estimated depreciation
expense at December 31, 2013 for each of the five succeeding years is as follows:

Demand notes payable to related parties
consist of various demand notes outstanding to stockholders totaling $1,750,000 and $1,337,500 at December 31, 2013 and 2012,
respectively. The primary lender is John N. Hatsopoulos, the company’s Chief Executive Officer, who holds $1,750,000 and
$1,300,000 of the demand notes as of December 31, 2013 and 2012, respectively. The demand notes accrue interest annually at
rates ranging from 5% to 6%. Unpaid principal and interest on the demand notes is due upon demand by the lender. On January 6,
2014, the Company repaid the then outstanding principal balance of $1,750,000 together with accrued interest of $175,311.

On September 24, 2001, the Company entered
into subscription agreements with three investors for the sale of convertible debentures in the aggregate principal amount of $330,000.
The primary investors were George N. Hatsopoulos, a member of the board of directors, who subscribed for $200,000 of the debentures
and John N. Hatsopoulos, the Company’s Chief Executive Officer, who subscribed for $100,000 of the debentures. The debentures
accrue interest at a rate of 6% per annum and are due six years from issuance date. The debentures are convertible, at the option
of the holder, into a number of shares of Common Stock as determined by dividing the original principal amount plus accrued and
unpaid interest by a conversion price of $1.20. On September 24, 2011 the remaining holders of the Company’s convertible
debentures agreed to amend the terms of the debentures and extend the due date from September 24, 2011 to September 24, 2013.

On May 11, 2009 the Company sold 1,400,000.00
shares in Ilios at $0.50 per share to George Hatsopoulos and John Hatsopoulos in exchange for the extinguishment of $427,432
in demand notes payable, $109,033 in convertible debentures and $163,535 in accrued interest. The difference between the Company’s
purchase price of the Ilios shares and the amount of debt forgiveness was recorded as additional paid-in capital.

F-15

On September 30, 2009, Joseph J. Ritchie
elected to convert $30,000 of the outstanding principal amount of the debenture, plus accrued interest of $14,433, into 37,028
shares of Common Stock at a conversion price of $1.20 per share.

On September 30, 2012, certain holders of
the debentures converted the principal amount of $100,000 and accrued interest in the amount of $6,100 into 85,242 shares of the
Company's Common Stock. At December 31, 2012 there were 75,806 shares of common stock issuable upon conversion of the Company’s
outstanding convertible debentures. At December 31, 2012, the principal amount of the Company’s convertible debentures
was $90,967 which was due on September 24, 2013.

On October 18, 2013, the remaining holder
of the debentures, George N. Hatsopoulos, converted the principal balance of $90,967 into 75,806 shares of the Company's common
stock at a conversion price of $1.20 per share. In addition, Mr. Hatsopoulos requested that the accrued interest earned in 2012
in the amount of $6,913 be converted into 2,161 shares of the Company's common stock at a conversion price of $3.20 per share and
that the accrued interest earned on or after January 1, 2013 in the amount of $4,367 be converted into 970 shares of the Company's
common stock at a conversion price of $4.50 per share.

On March 25, 2013, the Company entered into
a Revolving Line of Credit Agreement, or the Credit Agreement, with John N. Hatsopoulos, our Chief Executive Officer. Under the
terms of the Credit Agreement, as amended on August 13, 2013, Mr. Hatsopoulos has agreed to lend the Company up to an aggregate
of $1,500,000 from time to time, at the written request of the Company. Any amounts borrowed by the Company pursuant to the Credit
Agreement will bear interest at the Bank Prime Rate as quoted from time to time in the Wall Street Journal plus 1.5% per year.
Repayment of the principal amount borrowed pursuant to the Credit Agreement will be due on March 1, 2014. In addition, the company
may prepay accrued interest, provided that prepayment may not be made prior to January 1, 2014.The Credit Agreement terminated
on March 1, 2014. As of December 31, 2013 the Company has borrowed $1,200,000 pursuant to the Credit Agreement. On January
6, 2014, the Company repaid the then outstanding principal balance of $1,200,000 together with accrued interest of $25,347.

On December 23, 2013, the company entered
into a Senior Convertible Promissory Note (the "Note") with Michaelson Capital Special Finance Fund LP, ("Michaelson"),
for the principal amount of $3,000,000 with interest at 4% per annum for a term of three years. In the event of default such interest
rate shall accrue at 8% after the occurrence of the event of default and during continuance plus 2% after the occurrence and during
the continuance of any other event of default. The Note is a senior unsecured obligation which pays interest only on a monthly
basis in arrears at a rate of 4% per annum, unless earlier converted in accordance with the terms of the agreement prior to such
date. The principal amount, if not converted, is due on the third anniversary of the Note, December 31, 2016. The Note is senior
in right of payment to any unsecured indebtedness that is expressly subordinated in right of payment to the Note.

The principal balance of the Note, together
with any unpaid interest, is convertible into shares of the Company's common stock at 185.19 shares of our common stock per $1,000
principal amount of Note (equivalent to a conversion price of $5.40 per share) at the option of Michaelson. If at any time the
common stock of the Company is (1) trading on a national securities exchange, (2) qualifies for unrestricted resale under federal
securities laws and (3) the arithmetic average of the volume weighted average price of the Common Stock for the twenty consecutive
trading days preceding the Company's notice of mandatory conversion exceeds $150,000, the Company shall have the right to require
conversion of all of the then outstanding principal balance together with unpaid interest of this Note into the Company's common
stock based on the conversion price of $5.40 per share.

The Company may prepay all of the outstanding
principal and interest due and payable under this Note in full, at any time prior to the maturity date for an amount equal to 120%
of the then outstanding principal and interest due and payable as of the date of such prepayment.

F-16

Upon change of control, as defined by the
Note, at Michaelson's option, the obligations may be assumed, on the terms and conditions in this Note, through an assignment and
assumption agreement, or the Company may prepay all of the then outstanding principal and unpaid interest under this Note in full
at the optional 120% prepayment amount. This provision creates an embedded derivative in accordance with ASC 815, Derivatives
and Hedging. As such it is required to be bifurcated and accounted for separately from the Note. However, the Company
has determined that the fair value of the embedded derivative is immaterial to the financial statements.

Debt issuance costs of $140,433 are being
amortized to interest expense over the term of the Note using the effective interest method. At December 31, 2013, there were
555,556 shares of common stock issuable upon conversion of the Company’s outstanding convertible debentures.

Michaelson has the option to call the Note
upon an event of default at the optional 120% prepayment amount discussed above. One event of default is defined as the Company’s
failure to issue a registration statement covering the resale of the Company’s Common Stock that is declared effective within
one year of the funding date of the Note. The Company has classified this Note as current on the accompanying consolidated
balance sheet due to this event of default as the company cannot control when the registration statement, originally filed on February
6, 2014, will become effective. Additionally, the Note contains a contingent interest clause in connection with events of default,
including this event of default. This registration rights provision is not indexed to credit risk, and therefore is not clearly
and closely related to the Note. This provision creates an embedded derivative in accordance with ASC 815, Derivatives and Hedging. As
such it is required to be bifurcated and accounted for separately from the Note. However, the Company has determined that
the fair value of the embedded derivative is immaterial to the financial statements.

While, prior to this transaction, Michaelson
was an unrelated party, due to their beneficial ownership percentage of 6.4% after this transaction, Michaelson is now considered
a related party.

Note 8 – Commitments and contingencies

Operating Lease Obligations

The Company leases
office space and warehouse facilities under various lease agreements which expire through March 2024. The Company subleases portions
of its corporate offices and manufacturing facility to sub-tenants under annual sublease agreements, on a calendar year basis (see
Note 13 – Related party transactions). Total rent expense for the years ended December 31, 2013 and 2012 amounted
to $616,041 and $595,851, offset by $127,784 and $173,898 in rent paid by sub-lessees, to both related and unrelated parties, for
a net amount of $488,257 and $421,953.

As of December 31,
2013, the future minimum lease payments receivable on subleases were $51,033 on sub-leases.

The Company leased one service vehicle under
a lease agreement which expired January 2012. Vehicle rent expense amounted to $387 during the year ended December 31, 2012.

F-17

Future minimum lease payments under all
non-cancelable operating leases as of December 31, 2013 consist of the following:

Years Ending December 31,

Amount

2014

$

579,495

2015

535,349

2016

485,040

2017

491,920

2018

499,122

2019 and thereafter

2,742,217

Total

$

5,333,143

Letters of Credit

On October 26, 2011, the Company entered
into an agreement with Digital Energy Corp., a customer of the Company, whereby the Company provided a letter of credit in the
amount of $180,000, for the benefit of Digital Energy Corp., to satisfy a requirement of the New York Independent System Operator,
Inc. A certificate of deposit for $180,000 secures the letter of credit. In exchange for providing this letter of credit, Digital
Energy Corp. provided a promissory note to the Company for $180,000, with interest at 6%, payable in monthly installments of interest
only. Principal would only be owed if the letter of credit was drawn upon and would become due and payable on the first anniversary
date of the note. On February 19, 2013 this letter of credit and certificate of deposit restriction were released.

As of December 31, 2013, $583,073 in
a letter of credit was outstanding under a revolving bank credit facility needed to collateralize a performance bond on a certain
installation project. This revolving bank credit facility expires June 14, 2014. In addition, approximately $1,055,000 in
letters of credit were required to collateralize performance bonds on several installation projects. This letter of credit is collateralized
by an account owned by John N. Hatsopoulos and expires July 22, 2014. In each case, a performance bond has been furnished
on the project and would be drawn upon only in the event that Tecogen fails to complete the project in accordance with the contract.

Legal Proceedings

From time to time the Company may be involved
in various claims and other legal proceedings which arise in the normal course of business. Such matters are subject to many uncertainties
and outcomes that are not predictable. Based on the information available to the Company and after discussions with legal counsel,
the Company does not believe any such proceedings will have a material adverse effect on the business, results of operations, financial
position or liquidity.

Note 9 – Product warranty

The Company reserves an estimate of its
exposure to warranty claims based on both current and historical product sales data and warranty costs incurred. The majority of
the Company’s products carry a one-year warranty. The Company assesses the adequacy of its recorded warranty liability annually
and adjusts the amount as necessary. The warranty liability is included in accrued expenses on the accompanying consolidated balance
sheets.

F-18

Changes in the Company’s warranty
reserve were as follows:

Warranty reserve, December 31, 2011

$

57,000

Warranty provision for units sold

160,684

Costs of warranty incurred

(127,484

)

Warranty reserve, December 31, 2012

90,200

Warranty provision for units sold

179,841

Costs of warranty incurred

(175,041

)

Warranty reserve, December 31, 2013

$

95,000

Note 10 – Stockholders’ equity

Common Stock

In 2013 and 2012 the Company raised additional
funds through private placements of common stock to a limited number of accredited investors. In connection with the 2013 private
placements the Company sold an aggregate of 1,476,789 shares of common stock at a purchase price of $4.50 per share. In connection
with this private placement the Company incurred commissions, legal fees and various other costs of $678,746 which were offset
against the proceeds in additional paid in capital, resulting in net cash proceeds of $5,966,805. In connection with the 2012 private
placements the Company sold an aggregate of 212,500 shares of common stock at a purchase price $3.20 per share, resulting in net
cash proceeds after commissions and other offering costs of $680,000.

The holders of Common Stock have the right
to vote their interest on a per share basis. At December 31, 2013 and 2012 there were 15,156,600 and 13,611,974 shares of
Common Stock outstanding, respectively.

Preferred Stock

On February 13, 2013, the authorized preferred
stock of 10 million shares, as of December 31, 2013 none of these shares were issued or outstanding.

Receivable from Shareholder

On June 3, 2010 the Company issued a promissory
note to an investor in the amount of $345,000. The note was due in full on June 3, 2012 and bears interest at the Bank Prime Rate
plus three percent. Accrued interest is paid on a quarterly basis. The note was secured by 287,500 shares of Tecogen Common Stock.
The note was repaid with cash of $105,000 and return of 100,000 shares of common stock at a value of $2.40 per share, which were
retired by the Company on December 7, 2012.

Stock-Based Compensation

In 2006, the Company adopted the 2006 Stock
Option and Incentive Plan (the “Plan”), under which the board of directors may grant incentive or non-qualified stock
options and stock grants to key employees, directors, advisors and consultants of the Company. The Plan was amended at various
dates by the board to increase the reserved shares of common stock issuable under the Plan from 1,000,000 to 1,838,750 as of December 31,
2013 (the “Amended Plan”).

Stock options vest based upon the terms
within the individual option grants, with an acceleration of the unvested portion of such options upon a change in control event,
as defined in the Amended Plan. The options are not transferable except by will or domestic relations order. The option price per
share under the Amended Plan cannot be less than the fair market value of the underlying shares on the date of the grant. The number
of shares remaining available for future issuance under the Amended Plan as of December 31, 2013 and 2012 was 58,683 and 135,183,
respectively.

F-19

In 2012, the company granted nonqualified
options to purchase an aggregate of 17,500 shares of common stock at $3.20 per share to a director. These options have a vesting
schedule of four years and expire in ten years. The fair value of the options issued in 2012 was $20,223. The weighted-average
grant date fair value of stock options granted during 2012 was $1.16 per option.

In 2013, the company granted nonqualified
options to purchase an aggregate of 37,500 and 39,000 shares of common stock at $3.20 and $4.50 per share, respectively to certain
employees. These options have a vesting schedule of four years and expire in five and ten years, respectively. The fair value of
the options issued in 2013 was $80,952. The weighted-average grant date fair value of stock options granted during 2013 was $0.75
and $1.35 per option. Stock option activity for the years ended December 31, 2013 and 2012 was as follows:

Common Stock Options

Number of
Options

Exercise
Price Per Share

Weighted
Average
Exercise Price

Weighted Average
Remaining Life

Aggregate
Intrinsic Value

Outstanding, December 31, 2011

1,095,250

$0.12-$2.80

$

1.92

5.53 years

$

1,387,150

Granted

17,500

3.20

3.20

Exercised

—

—

—

Canceled and forfeited

(15,938

)

1.20 - 2.60

1.28

Expired

(313

)

2.60

2.60

Outstanding, December 31, 2012

1,096,500

$0.12-$3.20

$

1.96

4.66
years

$

1,356,400

Exercisable, December 31, 2012

662,563

$

1.56

$

1,096,225

Vested and expected to vest, December 31,
2012

1,096,500

$

1.96

$

1,356,400

Outstanding, December 31, 2012

1,096,500

$0.12-$3.20

$

1.96

4.66 years

$

1,356,400

Granted

76,500

3.20-4.50

3.86

Exercised

(25,000

)

0.12

0.12

Canceled and forfeited

—

—

—

Expired

—

—

—

Outstanding, December 31, 2013

1,148,000

$1.20-$4.50

$

2.13

5.80
years

$

2,721,100

Exercisable, December 31, 2013

799,500

$

1.79

$

2,166,550

Vested and expected to vest, December 31,
2013

1,148,000

$

2.13

$

2,721,100

The Company does not expect any forfeitures
and the table above represents all stock options expected to vest. The Company uses the Black-Scholes option pricing model to determine
the fair value of stock options granted. Use of a valuation model requires management to make certain assumptions with respect
to selected model inputs. Expected volatility was calculated based on the average volatility of four comparable publicly traded
companies. The average expected life was estimated using the simplified method to determine the expected life based on the vesting
period and contractual terms, since it does not have the necessary historical exercise data to determine an expected life for stock
options. The Company uses a single weighted-average expected life to value option awards and recognizes compensation on a straight-line
basis over the requisite service period for each separately vesting portion of the awards. The risk-free interest rate is based
on U.S. Treasury zero-coupon issues with a remaining term which approximates the expected life assumed at the date of grant.

F-20

The weighted average assumptions used in
the Black-Scholes option pricing model for options granted in 2013 and 2012 are as follows:

2013

2012

Stock option awards:

Expected life

5.63 years

6.25 years

Risk-free interest rate

1.34%

0.70%

Expected volatility

26.5%-36.1%

35.9%-36.0%

The Company has granted restricted stock
awards to its employees and directors. The performance based awards have vesting schedules ranging from 100% 90 days after an initial
public offering (IPO) up to 100% one year after an IPO.

Restricted stock activity for the years
ended December 31, 2013 and 2012 was as follows:

Number of Restricted Stock

Weighted Average Grant Date Fair Value

Unvested, December 31, 2011

483,317

$

1.44

Granted

—

—

Vested

—

—

Forfeited

(84,247

)

1.36

Unvested, December 31, 2012

399,070

$

1.44

Granted

—

—

Vested

—

—

Forfeited

(37,500

)

2.60

Unvested, December 31, 2013

361,570

$

1.31

During the years ended December 31,
2013 and 2012, the Company recognized stock-based compensation of $59,678 and $136,184, respectively, related to the issuance of
stock options and restricted stock. No tax benefit was recognized related to the stock-based compensation recorded during the years.
At December 31, 2013 and 2012 there were 361,570 and 399,070 unvested shares of restricted stock outstanding, respectively.
At December 31, 2013 and 2012 the total compensation cost related to unvested restricted stock awards and stock option awards
not yet recognized is $124,845 and $183,230, respectively. This amount will be recognized over a weighted average period of 0.56
years.

Stock Based Compensation - Ilios

In 2009, Ilios adopted the 2009 Stock Incentive
Plan (the “2009 Plan”) under which the board of directors may grant incentive or non-qualified stock options and stock
grants to key employees, directors, advisors and consultants of the company. The maximum number of shares allowable for issuance
under the Plan is 2,000,000 shares of common stock.

Stock options vest based upon the terms
within the individual option grants, with an acceleration of the unvested portion of such options upon a change in control event,
as defined in the Plan. The options are not transferable except by will or domestic relations order. The option price per share
under the Plan cannot be less than the fair market value of the underlying shares on the date of the grant.

In 2012, Ilios granted nonqualified options
to purchase 50,000 shares of common stock to a director at $0.50 per share. These options have a vesting schedule of four years
and expire in ten years. The total fair value of the options issued in 2012 was $9,750. The weighted-average grant date fair value
of stock options granted during 2012 was $0.20.

F-21

During the years ended December 31,
2013 and 2012 Ilios recognized stock-based compensation of $(41,311) and $59,361, related to the forfeiture and issuance of stock
options and restricted stock, respectively. No tax benefit was recognized related to the stock-based compensation recorded during
the year. At December 31, 2013 and 2012 there were 310,000 and 510,000 unvested shares of restricted stock outstanding. At
December 31, 2013 and 2012 the total compensation cost related to unvested restricted stock awards and stock option awards
not yet recognized is $9,004 and $67,493, respectively. This amount will be recognized over the weighted average period of 1.59
years.

Stock option activity relating to Ilios
for the year ended December 31, 2013 and 2012 was as follows:

Common Stock Options

Number of
Options

Exercise
Price Per Share

Weighted
Average
Exercise Price

Weighted Average
Remaining Life

Aggregate
Intrinsic Value

Outstanding, December 31, 2011

525,000

$0.10-$0.50

$

0.27

8.23 years

$

120,000

Granted

50,000

0.50

0.50

Exercised

—

—

—

Canceled and forfeited

—

—

—

Expired

—

—

—

Outstanding, December 31, 2012

575,000

$0.10-$0.50

$

0.29

7.44
years

$

120,000

Exercisable, December 31, 2012

—

$

—

$

—

Vested and expected to vest, December 31,
2012

575,000

$

0.29

$

120,000

Outstanding, December 31, 2012

575,000

$0.10-$0.50

$

0.29

7.44 years

$

120,000

Granted

—

—

—

Exercised

—

—

—

Canceled and forfeited

—

—

—

Expired

—

—

—

Outstanding, December 31, 2013

575,000

$0.10-$0.50

$

0.29

6.44
years

$

120,000

Exercisable, December 31, 2013

—

$

0.50

$

—

Vested and expected to vest, December 31,
2013

575,000

$

0.29

$

120,000

Ilios does not expect any forfeitures and
the table above represents all stock options expected to vest. Ilios uses the Black-Scholes option pricing model to determine the
fair value of stock options granted. Expected volatility was calculated based on the average volatility of comparable publicly
traded companies, the expected life of the options was calculated using the simplified method, and the risk-free interest rate
is based on U.S. Treasury zero-coupon issues with a remaining term which approximates the expected life assumed at the date of
grant. The Company uses a single weighted-average expected life to value option awards and recognizes compensation on a straight-line
basis over the requisite service period for each separately vesting portion of the awards.

For the Ilios awards, the weighted average
assumptions used in the Black-Scholes option pricing model for options granted in 2012 are as follows:

2012

Stock option awards:

Expected life

6.25 years

Risk-free interest rate

2.03

%

Expected volatility

36.1

%

F-22

Ilios has granted restricted stock awards
to its employees and directors. The awards have only service conditions and carry vesting schedules ranging from 100% 90 days after
an IPO up to 100% one year after an IPO.

Restricted stock activity for the Ilios
awards, for the years ended December 31, 2013 and 2012 was as follows:

Number of Restricted Stock

Weighted Average Grant Date Fair Value

Unvested, December 31, 2011

560,000

$

0.24

Granted

—

—

Vested

—

—

Forfeited

(50,000

)

0.10

Unvested, December 31, 2012

510,000

$

0.24

Granted

—

—

Vested

—

—

Forfeited

(200,000

)

0.50

Unvested, December 31, 2013

310,000

$

0.10

Note 11 – Noncontrolling interests

As of January 1, 2012 Tecogen owned 63.0%
of Ilios. During the year ended December 31, 2012 Tecogen purchased 1,000,000 shares of Ilios common stock at $0.50 per share
for an aggregate amount of $750,000 which increased Tecogen's ownership interest to 67.4%.

During the year ended December 31,
2012 Ilios sold 1,000,000 shares of common stock to an accredited investor at $0.50 per share for an aggregate amount of $500,000.
Also during the year ended December 31, 2012, Tecogen purchased 1,000,000 shares of Ilios common stock at $0.50 per share
for an aggregate amount of $500,000. The net result decreased Tecogen’s ownership interest to 65.0%. The table below presents
the changes in equity resulting from net loss attributable to Tecogen and transfers to or from noncontrolling interests for the
years ended December 31, 2013 and 2012.